Method and apparatus for enhanced control channel-based operation in wireless communication system

ABSTRACT

The present invention relates to a wireless communication system, and more specifically, to a method and an apparatus for enhanced control channel-based operation. A method for a base station for transmitting a downlink control channel in a wireless communication system according to one embodiment of the present invention comprises the steps of: determining one antenna port to be used for the downlink control channel; mapping the downlink control channel to a resource element on the basis of a reference signal for the one antenna port; and transmitting the mapped downlink control channel to a terminal, wherein an index for the one antenna port can be determined on the basis of a control channel element (CCE) index of the downlink control channel derived from the terminal identifier.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for an enhanced-controlchannel-based operation.

BACKGROUND ART

A user equipment (UE) detects a downlink (DL) control channel forcarrying scheduling information about DL data transmission andaccordingly receives DL data from an eNB. The UE generatesacknowledgement/negative-acknowledgement (ACK/NACK) informationindicating whether decoding of DL data is successful and transmits theACK/NACK information to the eNB.

In a conventional wireless communication system, a resource used fortransmission of ACK/NACK information may be determined from a DL controlchannel for carrying the DL scheduling information. In addition, in theconventional wireless communication system, the DL control channel istransmitted based on an antenna port of a cell-specific referencesignal, and a UE detects and demodulates the DL control channel based onan estimated channel using an antenna port of the cell-specificreference signal.

DISCLOSURE Technical Problem

In an enhanced wireless communication system, an enhanced physicaldownlink control channel (E-PDCCH) may be used. The E-PDCCH may betransmitted based on a demodulation reference (DMRS) but not acell-specific reference signal and may support multi-user multiple inputmultiple output (MU-MIMO).

When a method of determining a resource for transmission ofacknowledgement/negative-acknowledgement (ACK/NACK) is used, a problemarises in that the same resource for transmission of ACK/NACKinformation about downlink (DL) data transmitted according to differentpieces of scheduling information may be determined (i.e., collision). Inaddition, when one E-PDCCH is transmitted using a plurality of resourceregions, since antenna ports corresponding to the respective resourceregions are different, an antenna port as a reference is determined inorder to appropriately perform E-PDCCH transmission of an eNB andE-PDCCH demodulation of a UE.

The present invention provides a method of effectively and appropriatelydetermining an uplink (UL) ACK/NACK transmission resource in relation toan E-PDCCH. In addition, the present invention also provides a method ofaccurately determining an antenna port in relation to an E-PDCCH tosupport an appropriate operation by a transmitter and receiver of theE-PDCCH.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Technical Solution

The object of the present invention can be achieved by providing amethod of transmitting a downlink (DL) control channel by an eNB in awireless communication system, the method including determining oneantenna port used in the DL control channel, mapping the DL controlchannel to a resource element using the one antenna port, andtransmitting the mapped DL control channel to a user equipment (UE),wherein an index of the one antenna port is determined based on an indexof a control channel element (CCE) of the DL control channel, derivedfrom an identifier of the UE.

In another aspect of the present invention, provided herein is a methodof receiving a downlink (DL) control channel by a user equipment (UE) ina wireless communication system, the method including determining oneantenna port used for the DL control channel, and demodulating the DLcontrol channel based on a reference signal for the one antenna port,wherein an index of the one antenna port is determined based on an indexof a control channel element (CCE) of the DL control channel, derivedfrom an identifier of the UE.

In another aspect of the present invention, provided herein is an eNBfor transmitting a downlink (DL) control channel in a wirelesscommunication system, the eNB including a receiver, a transmitter, and aprocessor, wherein the processor is configured to determine one antennaport used in the DL control channel, to map the DL control channel to aresource element using the one antenna port, and to transmit the mappedDL control channel to a user equipment (UE) using the transmitter, andan index of the one antenna port is determined based on an index of acontrol channel element (CCE) of the DL control channel, derived from anidentifier of the UE.

In another aspect of the present invention, provided herein is a userequipment (UE) for receiving a downlink (DL) control channel in awireless communication system, the UE including a receiver, atransmitter, and a processor, wherein the processor is configured todetermine one antenna port used in the DL control channel and todemodulate the DL control channel based on a reference signal for theone antenna port, and an index of the one antenna port is determinedbased on an index of a control channel element (CCE) of the DL controlchannel, derived from an identifier of the UE.

The following features can be commonly applied to embodiments of thepresent invention.

The index of the one antenna port may be determined to correspond to anindex of one CCE derived from the identifier of the UE among a pluralityof CCEs of the DL control channel.

The index of the one CCE derived from the identifier of the UE may ben′, n′=(n_(CCE) mod d)+(X mod min (L,d)), n_(CCE) may be a lowest valueamong CCE indexes used for transmission of the DL control channel, d maybe a number of CCEs formed on one resource block pair, X may be theidentifier of the UE, L may be an aggregation level of the DL controlchannel, mod may be modulo calculation, and min(L,d) may be a minimumvalue of L and d.

The identifier of the UE may be n_(RNTI).

The index of the one antenna port may be AP, AP=p+n′, and p may be aminimum value of antenna port indexes available for the DL controlchannel.

The index of the one antenna port may be AP, AP=p+n′*2, and p may be aminimum value of antenna port indexes available for the DL controlchannel.

The index of the one antenna port may be AP, AP=p+n′ when a number ofCCEs defined in one resource block may be 4; AP=p+n′*2 when a number ofCCEs defined in one resource block is 2, and p may be a minimum value ofantenna port indexes available for the DL control channel.

An available antenna port index for the UL control channel may be 107,108, 109, and 110.

An aggregation level of the DL control channel may be equal to orgreater than 2.

The DL control channel may be transmitted in a localized manner.

The DL control channel may be an enhanced-physical downlink controlchannel (E-PDCCH), and the CCE may be an enhanced CCE (ECCE).

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

The present invention provides a method of effectively and appropriatelydetermining an uplink (UL) acknowledgement/negative-acknowledgement(ACK/NACK) transmission resource in relation to an E-PDCCH. In addition,the present invention also provides a method of accurately determiningan antenna port in relation to an E-PDCCH to support an appropriateoperation by a transmitter and receiver of the E-PDCCH.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description taken in conjunction with theaccompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a diagram illustrating a structure of a radio frame;

FIG. 2 is a diagram illustrating a resource grid;

FIG. 3 is a diagram illustrating a structure of a downlink (DL)subframe;

FIG. 4 is a diagram illustrating a structure of a uplink (UL) subframe;

FIG. 5 is a diagram for explanation of a DL reference signal;

FIGS. 6 and 7 are diagrams for explanation of an operation ofdemodulating an E-PDCCH transmitted through a plurality of resourceregions using a representative antenna port according to an embodimentof the present invention;

FIG. 8 is a diagram for explanation of an operation of demodulating anE-PDCCH transmitted through a plurality of resource regions using arepresentative antenna port according to another embodiment of thepresent invention;

FIGS. 9 and 10 are flowcharts for explanation of an E-PDCCH-basedoperation method according to embodiments of the present invention; and

FIG. 11 illustrates configurations of an eNB and a user equipment (UE)according to an embodiment of the present invention.

BEST MODE

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered optional factors on the conditionthat there is no additional remark. If required, the individualconstituent components or characteristics may not be combined with othercomponents or characteristics. Also, some constituent components and/orcharacteristics may be combined to implement the embodiments of thepresent invention. The order of operations to be disclosed in theembodiments of the present invention may be changed. Some components orcharacteristics of any embodiment may also be included in otherembodiments, or may be replaced with those of the other embodiments asnecessary.

The embodiments of the present invention are disclosed on the basis of adata communication relationship between a base station and a terminal.In this case, the base station is used as a terminal node of a networkvia which the base station can directly communicate with the terminal.Specific operations to be conducted by the base station in the presentinvention may also be conducted by an upper node of the base station asnecessary.

In other words, it will be obvious to those skilled in the art thatvarious operations for enabling the base station to communicate with theterminal in a network composed of several network nodes including thebase station will be conducted by the base station or other networknodes other than the base station. The term “base station (BS)” may bereplaced with a fixed station, Node-B, eNode-B (eNB), or an access pointas necessary. The term “relay” may be replaced with the terms relay node(RN) or relay station (RS). The term “terminal” may also be replacedwith a user equipment (UE), a mobile station (MS), a mobile subscriberstation (MSS) or a subscriber station (SS) as necessary.

It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to other formats within the technical scope orspirit of the present invention.

In some instances, well-known structures and devices are omitted inorder to avoid obscuring the concepts of the present invention andimportant functions of the structures and devices are shown in blockdiagram form. The same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments disclosed for at least one of wireless access systemsincluding an institute of electrical and electronics engineers (IEEE)802 system, a 3rd generation partnership project (3GPP) system, a 3GPPlong term evolution (LTE) system, an LTE-advanced (LTE-A) system, and a3GPP2 system. In particular, steps or parts, which are not described toclearly reveal the technical idea of the present invention, in theembodiments of the present invention may be supported by the abovedocuments. All terminology used herein may be supported by at least oneof the above-mentioned documents.

The following embodiments of the present invention can be applied to avariety of wireless access technologies, for example, code divisionmultiple access (CDMA), frequency division multiple access (FDMA), timedivision multiple access (TDMA), orthogonal frequency division multipleaccess (OFDMA), single carrier frequency division multiple access(SC-FDMA), and the like. CDMA may be embodied through wireless (orradio) technology such as universal terrestrial radio access (utra) orCDMA2000. TDMA may be embodied through wireless (or radio) technologysuch as global system for mobile communication (GSM)/general packetradio service (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMAmay be embodied through wireless (or radio) technology such as instituteof electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802-20, and evolved UTRA (E-UTRA). UTRA is a partof universal mobile telecommunications system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of E-UMTS(Evolved UMTS), which uses E-UTRA. 3GPP LTE employs OFDMA in downlink(DL) and employs SC-FDMA in uplink (UL). LTE-Advanced (LTE-A) is anevolved version of 3GPP LTE. WiMAX can be explained by IEEE 802.16e(wirelessMAN-OFDMA reference system) and advanced IEEE 802.16m(wirelessMAN-OFDMA advanced system). For clarity, the followingdescription focuses on IEEE 802.11 systems. However, technical featuresof the present invention are not limited thereto.

Radio Frame Structure

With reference to FIG. 1, a structure of a radio frame of a 3GPP LTEsystem will be described below.

In a cellular orthogonal frequency division multiplexing (OFDM) wirelesspacket communication system, UL/DL data packets are transmitted insubframes. One subframe is defined as a predetermined time intervalincluding a plurality of OFDM symbols. The 3GPP LTE standard supports atype 1 radio frame structure applicable to frequency division duplex(FDD) and a type 2 radio frame structure applicable to time divisionduplex (TDD).

FIG. 1(a) is a diagram illustrating the structure of the type 1 radioframe. One radio frame includes 10 subframes, each subframe includingtwo slots in the time domain. A time required for transmitting onesubframe is defined as a transmission time interval (TTI). For example,one subframe may be 1 ms long and one slot may be 0.5 ms long. One slotincludes a plurality of OFDM symbols in the time domain and a pluralityof resource blocks (RBs) in the frequency domain. Since the 3GPP LTEsystem uses OFDMA for DL, an OFDM symbol may be one symbol period. TheOFDM symbol may be called an SC-FDMA symbol or symbol period. An RB is aresource allocation unit including a plurality of contiguous subcarriersin one slot.

The number of OFDM symbols included in one slot may be changed accordingto the configuration of a cyclic prefix (CP). There are two types ofCPs, extended CP and normal CP. For example, if each OFDM symbol isconfigured to include a normal CP, one slot may include 7 OFDM symbols.If each OFDM symbol is configured to include an extended CP, the lengthof an OFDM symbol is increased and thus the number of OFDM symbolsincluded in one slot is less than that in the case of a normal CP. Inthe case of the extended CP, for example, one slot may include 6 OFDMsymbols. If a channel state is instable as is the case with a fast UE,the extended CP may be used in order to further reduce inter-symbolinterference.

FIG. 1(b) illustrates the structure of the type 2 radio frame. The type2 radio frame includes two half frames, each half frame including 5subframes, a DL pilot time slot (DwPTS), a guard period (GP), and a ULpilot time slot (UpPTS). One subframe is divided into two slots. TheDwPTS is used for initial cell search, synchronization, or channelestimation at a UE, and the UpPTS is used for channel estimation and ULtransmission synchronization with a UE at an eNB. The GP is used tocancel UL interference between UL and DL, caused by the multi-path delayof a DL signal. One subframe includes two slots irrespective of a typeof radio frame.

The aforementioned radio frame structure is purely exemplary. The numberof subframes included in a radio frame or the number of slots includedin each subframe, and the number of symbols of each slot can be changedin various ways.

FIG. 2 illustrates the structure of a DL resource grid for the durationof one DL slot. One DL slot includes 7 OFDM symbols in the time domainand one resource block includes 12 subcarriers in the frequency domain,which is purely exemplary, but embodiments of the present invention arenot limited thereto. For example, in the case of normal cyclic prefix(CP), one slot may include 7 OFDM symbols, but in the case ofextended-CP, one slot may include 6 OFDM symbols. Each element of theresource grid is referred to as a resource element (RE). One resourceblock includes 12×7 REs. The number of RBs in a DL slot, N^(DL) dependson a DL transmission bandwidth. A UL slot may have the same structure asa DL slot.

DL Subframe Structure

FIG. 3 illustrates a structure of a DL subframe. Up to three or fourOFDM symbols at the start of the first slot of a DL subframe are used asa control region to which control channels are allocated and the otherOFDM symbols of the DL subframe are used as a data region to which aPDSCH is allocated. DL control channels defined for the 3GPP LTE systeminclude a physical control format indicator channel (PCFICH), a physicaldownlink control channel (PDCCH), and a physical hybrid-ARQ indicatorchannel (PHICH). The PCFICH is located in the first OFDM symbol of asubframe, carrying information about the number of OFDM symbols used fortransmission of control channels in the subframe. The PHICH delivers anHARQ acknowledgement/negative-acknowledgement (ACK/NACK) signal as aresponse to a UL transmission. Control information carried on the PDCCHis called downlink control information (DCI). The DCI includes UL or DLscheduling information, UL transmission power control commands for arandom UE group.

The PDCCH delivers information about resource allocation and a transportformat for a downlink shared channel (DL-SCH), information aboutresource allocation and a transport format for an uplink shared channel(UL-SCH), paging information of a paging channel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a random access responsetransmitted on the PDSCH, a set of Tx power control commands forindividual UEs of a UE group, Tx power control commands, voice overInternet protocol (VoIP) activation indication information, etc. Aplurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. A PDCCH is transmitted in an aggregate ofone or more consecutive Control Channel Elements (CCEs). A CCE is alogical allocation unit used to provide a PDCCH at a coding rate basedon the state of a radio channel. A CCE includes a plurality of RE groups(REGs). The format of a PDCCH and the number of available bits for thePDCCH are determined according to the number of CCEs and a coding rateprovided by the CCEs. An eNB determines a PDCCH format according to DCItransmitted to a UE and adds a cyclic redundancy check (CRC) to controlinformation. The CRC is masked by an identifier (ID) known as a radionetwork temporary identifier (RNTI) according to the owner or usage ofthe PDCCH. If the PDCCH is destined for a specific UE, the CRC may bemasked by a cell-RNTI (C-RNTI) of the UE. If the PDCCH carries a pagingmessage, the CRC of the PDCCH may be masked by a paging indicatoridentifier (P-RNTI). If the PDCCH carries system information,particularly, a system information block (SIB), its CRC may be masked bya system information ID and a system information RNTI (SI-RNTI). Toindicate that the PDCCH carries a random access response to a randomaccess preamble transmitted by a UE, its CRC may be masked by a randomaccess-RNTI (RA-RNTI).

PDCCH Processing

In PDCCH transmission, control channel elements (CCEs), contiguouslogical allocation units, are used to map a PDCCH to REs. One CCEincludes a plurality of (e.g., 9) REGs and one REG includes fourneighboring REs except for a RS.

The number of CCEs necessary for a specific PDCCH depends on a DCIpayload corresponding to a control information size, a cell bandwidth, achannel coding rate, etc. Specifically, the number of CCEs for aspecific PDCCH can be defined according to PDCCH format, as shown inTable 1 below.

TABLE 1 Number PDCCH Number Number of PDCCH format of CCEs of REGs bits0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

While one of the above-mentioned PDCCH formats may be used, this is notsignaled to a UE. Accordingly, the UE performs decoding without knowingthe PDCCH format, which is referred to as blind decoding. Sinceoperation overhead is generated if a UE decodes all CCEs that can beused for downlink for each PDCCH, a search space is defined inconsideration of limitation for a scheduler and the number of decodingattempts.

That is, the search space is a set of candidate PDCCHs composed of CCEson which a UE needs to attempt to perform decoding at an aggregationlevel. The aggregation level and the number of candidate PDCCHs can bedefined as shown in Table 2 below.

TABLE 2 Search space The number Aggregation Size of PDCCH level (CCEunit) candidates UE-specific 1 6 6 2 12 6 4 8 2 8 16 2 Common 4 16 4 816 2

As shown Table 2, the UE has a plurality of search spaces at eachaggregation level because 4 aggregation levels are present. The searchspaces may be divided into a UE-specific search space and a commonsearch space, as shown in Table 2. The UE-specific search space is for aspecific UE. Each UE may check an RNTI and CRC which mask a PDCCH bymonitoring a UE-specific search space thereof (attempting to decode aPDCCH candidate set according to an available DCI format) and acquirecontrol information when the RNTI and CRC are valid.

The common search space is used for a case in which a plurality of UEsor all UEs needs to receive PDCCHs, for system information dynamicscheduling or paging messages, for example. The common search space maybe used for a specific UE for resource management. Furthermore, thecommon search space may overlap with the UE-specific search space.

As described above, the UE attempts to decode a search space. In thisregard, a number of times of decoding are determined according to atransmission mode determined via radio resource control (RRC) signalingand a DCI format. When carrier aggregation is not applied, the UE needsto consider two DCI sizes (DCI format 0/1A/3/3A and DCI format 1C) foreach of 6 PDCCH candidates with respect to the common search space, andthus, up to 12 decoding attempts are required. With respect to theUE-specific search space, two DCI sizes are considered for a PDCCHcandidate number (6+6+2+2=16), up to 32 decoding attempts are required.Accordingly, when carrier aggregation is not applied, up to 44 decodingattempts are required.

Enhanced-Control Channel

As an example of an enhanced-control channel, an enhanced-PDCCH(E-PDCCH) will be described below.

Control information included in the aforementioned DCI formats has beendescribed in terms of a case in which the control information istransmitted through a PDCCH defined in LTE/LTE-A. However, the controlinformation can be applied to another DL control channel, for example,an E-PDCCH instead of the PDCCH. The E-PDCCH may correspond to a newform of a control channel for carrying DCI such as scheduling allocationfor the UE and may be introduced in order to effectively support ascheme such as inter-cell interference coordination (ICIC), CoMP,MU-MIMO, etc.

The E-PDCCH is differentiated from a legacy PDCCH in that the E-PDCCH isallocated to a time-frequency resource region (e.g., the data region ofFIG. 3) except for a region (e.g., the control region of FIG. 3) definedfor PDCCH transmission in a legacy LTE/LTE-A system (hereinafter,referred to as a legacy-PDCCH in order to differentiate the legacy PDCCHfrom the E-PDCCH)). For example, mapping of resource elements of theE-PDCCH may be expressed as mapping the resource elements to OFDMsymbols except for first N (e.g., N≤4) of a DL subframe in the timedomain and mapping the resource elements to a set of semi-staticallyallocated resource blocks (RBs) in the frequency domain.

For a similar reason to the introduction of the E-PDCCH, an E-PHICH maybe defined as a new control channel for carrying HARQ ACK/NACKinformation for UL transmission and an E-PCFICH may be defined as a newcontrol channel for carrying information for a resource region used forDL control channel transmission. The E-PDCCH, the E-PHICH, and/or theE-PCFICH will be collectively referred to as an enhanced-controlchannel.

An enhanced REG may be used to define mapping to resource elements ofenhanced-control channels. For example, for one physical resource block(PRB) pair, 16 EREGs (that is, EREG 0 to EREG 15) may be present. On onePRB, remaining REs except for REs to which demodulation referencesignals (DMRSs) are mapped are denoted by numerals 0 to 15. An order inwhich the numerals are denoted is determined by an order in whichfrequency increases and then is determined by an order in which timeincreases. For example, REs denoted by a numeral i constitute one EREGi.

The enhanced-control channel may be transmitted using aggregation of oneor a plurality of enhanced CCEs (ECCEs). Each ECCE may include one or aplurality of EREGs. The number of EREGs per ECCE may be, for example, 4or 8 (4 in the case of a general subframe of a normal CP).

Available ECCEs for the enhanced-control channel may be denoted by 0 toN_(ECCE)−1. N_(ECCE) may be, for example, 1, 2, 4, 8, 16, or 32.

The number of REs of the PRB pair configured for transmission of theenhanced-control channel may be defined to satisfy the followingconditions i), ii), and iii): i) the REs are contained in one of 16EREGs of a PRB pair; ii) the REs are not used for a cell-specificreference signal (CRS) or a channel state information-reference signal(CSI-RS); and iii) the enhanced-control channel belongs to an OFDMsymbol with an index that is equal to or greater than an OFDM in which acontrol channel is started.

In addition, the enhanced-control channel may be mapped to REs using alocalized scheme or a distributed method. The enhanced-control channelmay be mapped to REs that satisfy the following conditions a) to d): a)the REs are contained in an EREG allocated for transmission; b) the REsare not contained in a PRB pair used for transmission of a physicalbroadcast channel (PBCH) or a synchronization signal; c) the REs are notused for a CRS or a CSI-RS for a specific UE; and d) theenhanced-control channel belongs to an OFDM symbol with an index that isequal to or greater than an OFDM in which a control channel is started.

Allocation of the enhanced-control channel may be performed as follows.One or a plurality of enhanced-control channel-PRB-set may be configuredfor the UE via higher layer signaling from an eNB. For example, in thecase of the E-PDCCH, the enhanced-control channel-PRB-set may be formonitoring of the E-PDCCH.

In addition, cross interleaving may or may not be applied to RE mappingof the enhanced-control channel.

When the cross interleaving is not applied, one enhanced-control channelmay be mapped to a specific set of a resource block, and the number ofresource blocks included in the set of the resource block may correspondto an aggregation level 1, 2, 4, or 8. In addition, anotherenhanced-control channel may not be transmitted in a correspondingresource block set.

When the cross interleaving is applied, a plurality of enhanced-controlchannels may be multiplexed and interleaved together and mapped to aresource block allocated for enhanced-control channel transmission. Thatis, it may also be expressed by mapping a plurality of enhanced-controlchannels together on a specific resource block set.

UL Subframe Structure

FIG. 4 illustrates a structure of a UL subframe. A UL subframe may bedivided into a control region and a data region in the frequency domain.The control region includes a PUCCH that carriers UL controlinformation. The data region includes a PUSCH that carrier user data. Inorder to maintain single carrier wave properties, one UE may notsimultaneously transmit a PUCCH and a PUSCH. An RB pair is allocated toa PUCCH of one UE in a subframe. RBs included in an RB pair occupydifferent subcarriers in two respective slots. The RB pair allocated tothe PUCCH frequency-hops over a slot boundary.

Reference Signal (RS)

In a mobile communication system, a packet is transmitted on a radiochannel from a transmitter to a receiver. In view of the nature of theradio channel, the packet may be distorted during the transmission. Toreceive the signal successfully, the receiver should compensate for thedistortion in the received signal using channel information. Generally,to enable the receiver to acquire the channel information, thetransmitter transmits a signal known to both the transmitter and thereceiver and the receiver acquires knowledge of channel informationbased on the distortion of the signal received on the radio channel. Thesignal known to both the transmitter and receiver is referred to as apilot signal or a reference signal (RS).

In transmission and reception of data using multiple antennas, thereceiver needs to know channel states between transmit antennas andreceive antennas. Accordingly, a separate reference signal is needed foreach transmit antenna.

A DL RS includes a common reference signal (CRS) shared by all UEs in acell and a dedicated reference signal (DRS) for a specific UE only.Information for channel estimation and demodulation can be providedaccording to the RSs. The CRS is an RS that can be commonly received byall UEs in a cell and distributed over all bands. The CRS can be usedfor CSI acquisition and data demodulation.

A receiver (UE) may estimate a channel state from the CRS and feedbackan indicator associated with channel quality, such as a channel qualityindicator (CQI), a precoding matrix index (PMI), and/or a rank indicator(RI) to a transmitter (eNB). The CRS can also be called a cell-specificRS.

The DRS can be transmitted through a corresponding RE when demodulationof data on a PDSCH is needed. The UE may receive information aboutpresence or absence of a DRS from a higher layer and receive informationrepresenting that the DRS is valid only when a corresponding PDSCH ismapped. The DRS may also be called a UE-specific reference signal ormodulation reference signal (DMRS). The DRS (or UE-specific referencesignal) is used for data demodulation. A precoding weight used for aspecific UE is used for the DRS during multi-antenna transmission suchthat an equivalent channel corresponding a combination of a precodingweight transmitted through each transmit antenna and a transmissionchannel can be estimated when the UE receives the DRS.

FIG. 5 illustrates a pattern of matching a CRS and a DRS defined in a3GPP LTE system (e.g. release-8) to a downlink RB pair. A downlink RBpair as a unit to which a reference signal is mapped can be representedby a product of one subframe in the time domain and 12 subcarriers inthe frequency domain. That is, one RB pair has a length corresponding to14 OFDM symbols in case of normal CP and a length corresponding to 12OFDM symbols in case of extended CP. FIG. 5 shows an RB pair in case ofnormal CP.

FIG. 5 shows positions of reference signals on an RB pair in a system inwhich an eNB supports four transmit antennas. In FIG. 5, REs denoted by‘R0’, ‘R1’, ‘R2’ and ‘R3’ correspond to CRS positions for antenna portindexes 0, 1, 2 and 3. In FIG. 5, REs denoted by ‘D’ correspond to DRSpositions.

High-order multiple input multiple output (MIMO), multi-celltransmission, enhanced multi-user (MU)-MIMO, etc. are considered inLTE-A evolved from 3GPP LTE. To efficiently operate reference signalsand support enhanced transmission schemes, DRS based data demodulationis being considered. That is, a DRS (or UE-specific reference signal orDMRS) for two or more layers can be defined to support data transmissionthrough an additional antenna, separately from a DRS (corresponding toantenna port index 5) for rank 1 beamforming defined in 3GPP LTE (e.g.release-8). For example, UE-specific reference signal ports supportingup to 8 transmit antenna ports can be defined as antenna port numbers 7to 12 and can be transmitted in REs which do not overlap with otherreference signals.

Furthermore, LTE-A may separately define an RS related to feedback ofchannel state information (CSI) such as CQI/PMI/RI for a new antennaport as a CSI-RS. For example, CSI-RS ports supporting up to 8 transmitantenna ports can be defined as antenna port numbers 15 to 22 and can betransmitted in REs which do not overlap with other reference signals.

Coordinated Multi-Point (CoMP)

CoMP transmission/reception scheme (which is also referred to asco-MIMO, collaborative MIMO or network MIMO) is proposed to meetenhanced system performance requirements of 3GPP LTE-A. CoMP can improvethe performance of a UE located at a cell edge and increase averagesector throughput.

In a multi-cell environment having a frequency reuse factor of 1, theperformance of a UE located at a cell edge and average sector throughputmay decrease due to inter-cell interference (ICI). To reduce ICI, aconventional LTE system uses a method for allowing a UE located at acell edge in an interfered environment to have appropriate throughputusing a simple passive scheme such as fractional frequency reuse (FFR)through UE-specific power control. However, it may be more preferable toreduce ICI or reuse ICI as a signal that a UE desires rather thandecreasing frequency resource use per cell. To achieve this, CoMP can beapplied.

CoMP applicable to downlink can be classified into joint processing (JP)and coordinated scheduling/beamforming (CS/CB).

According to the JP, each point (eNB) of a CoMP coordination unit canuse data. The CoMP coordination unit refers to a set of eNBs used for acoordinated transmission scheme. The JP can be divided into jointtransmission and dynamic cell selection.

The joint transmission refers to a scheme through which PDSCHs aresimultaneously transmitted from a plurality of points (some or all CoMPcoordination units). That is, data can be transmitted to a single UEfrom a plurality of transmission points. According to jointtransmission, quality of a received signal can be improved coherently ornon-coherently and interference on other UEs can be actively erased.

Dynamic cell selection refers to a scheme by which a PDSCH istransmitted from one point (in a CoMP coordination unit). That is, datais transmitted to a single UE from a single point at a specific time,other points in the coordination unit do not transmit data to the UE atthe time, and the point that transmits the data to the UE can bedynamically selected.

According to the CS/CB scheme, CoMP coordination units cancollaboratively perform beamforming of data transmission to a single UE.Here, user scheduling/beaming can be determined according tocoordination of cells in a corresponding CoMP coordination unit althoughdata is transmitted only from a serving cell.

In case of uplink, coordinated multi-point reception refers to receptionof a signal transmitted according to coordination of a plurality ofpoints geographically spaced apart from one another. A CoMP receptionscheme applicable to uplink can be classified into joint reception (JR)and coordinated scheduling/beamforming (CS/CB).

JR is a scheme by which a plurality of reception points receives asignal transmitted over a PUSCH and CS/CB is a scheme by which userscheduling/beamforming is determined according to coordination of cellsin a corresponding CoMP coordination unit while one point receives aPUSCH.

A UE can receive data from multi-cell base stations collaborativelyusing the CoMP system. The base stations can simultaneously support oneor more UEs using the same radio frequency resource, improving systemperformance. Furthermore, a base station may perform space divisionmultiple access (SDMA) on the basis of CSI between the base station anda UE.

In the CoMP system, a serving eNB and one or more collaborative eNBs areconnected to a scheduler through a backbone network. The scheduler canoperate by receiving channel information about a channel state betweeneach UE and each collaborative eNB, measured by each eNB, through thebackbone network. For example, the scheduler can schedule informationfor collaborative MIMO operation for the serving eNB and one or morecollaborative eNBs. That is, the scheduler can directly directcollaborative MIMO operation to each eNB.

As described above, the CoMP system can be regarded as a virtual MIMOsystem using a group of a plurality of cells. Basically, a communicationscheme of MIMO using multiple antennas can be applied to CoMP.

Determination of Transmission Resource of ACK/NACK Information

The ACK/NACK information is control information that is fed back to atransmitter from a receiver according to whether decoding of datatransmitted from the transmitter is successful. For example, whendecoding of DL data of a UE is successful, the UE may feedback ACKinformation to an eNB and otherwise feedback NACK information to theeNB. In detail, in an LTE system, there may be three cases in which thereceiver needs to transmit ACK/NACK, which will be described below.

First, ACK/NACK is transmitted in response to transmission of a PDSCHindicated by detection of a PDCCH. Second, ACK/NACK is transmitted inresponse to a PDCCH indicating release of semi-persistent scheduling(SPS). Third, ACK/NACK is transmitted in response to a PDSCH transmittedwithout detection of a PDCCH, which refers to ACK/NACK to transmissionof an SPS PDSCH. Hereinafter, unless specifically described, theACK/NACK transmission scheme is not limited to any one of theaforementioned three cases.

Hereinafter, transmission resources of ACK/NACK information in an FDDscheme and a TDD scheme will be described in detail.

The FDD scheme is a scheme of separating DL and UL for each respectiveindependent frequency band and performing transmission and reception.Accordingly, when an eNB transmits a PDSCH in a DL band, a UE maytransmit ACK/NACK response indicating whether DL data reception issuccessful via a PUCCH on a UL band corresponding to the DL band after aspecific period of time. Accordingly, the UE may operate with DL and ULhaving one to one correspondence.

In detail, in an example of a legacy 3GPP LTE system, controlinformation about DL data transmission of the eNB may be transmitted tothe UE through a PDCCH, and the UE that receives data, which isscheduled to the UE through the PDCCH, through a PDSCH may transmitACK/NACK through a PUCCH as a channel for transmission of UL controlinformation (or in a piggyback manner on a PUSCH). In general, a PUCCHfor transmission of ACK/NACK is not pre-allocated to each UE but insteada plurality of UEs in a cell uses a plurality of PUCCHs separated forrespective points of time. Accordingly, as a PUCCH resource in which aUE that receives DL data at a random point of time, a PUCCH resourcecorresponding to a PDCCH in which the UE receives scheduling informationof the corresponding DL data may be used.

The PUCCH resource corresponding to the PDCCH will be described in moredetail. A region in which a PDCCH of each DL subframe is transmittedincludes a plurality of control channel elements (CCEs), and a PDCCHtransmitted to one UE in a random subframe includes one or a pluralityof CCEs among CCEs constituting a PDCCH region of the subframe. Inaddition, in a region in which a PUCCH of each UL subframe istransmitted, resources for transmission of a plurality of PUCCHs arepresent. In this case, the UE may transmit ACK/NACK through a PUCCH withan index corresponding to an index of a specific CCE (e.g., a first orlowest CCE) among CCEs constituting a PDCCH received by the UE.

For example, it may be assumed that information on a PDSCH is deliveredon a PDCCH composed of CCEs #4, #5 and #6. In this case, a UE transmitsan ACK/NACK signal on PUCCH #4 corresponding to CCE #4, the first (orthe lowest) CCE of the PDCCH that schedules the PDSCH.

In an FDD system, the UE may transmit HARQ ACK/NACK information in asubframe index n in response to transmission of a PDSCH received in asubframe index (n−k) (e.g., k=4 in an LTE system). Based on a PDCCHindicating transmission of a PDSCH in a subframe (n−k), the UE maydetermine a PUCCH resource index for transmission of HARQ ACK/NACK in asubframe n.

For example, a PUCCH resource index in an LTE system is determined asfollows.

n ⁽¹⁾ _(PUCCH) =n _(CCE) N ⁽¹⁾ _(PUCCH)  [Equation 1]

In Equation 1 above, n⁽¹⁾ _(PUCCH) represents a resource index of PUCCHformat 1 for ACK/NACK/DTX transmission, N⁽¹⁾ _(PUCCH) denotes asignaling value received from a higher layer, and n_(CCE) denotes thesmallest value of CCE indexes used for PDCCH transmission. A cyclicshift, an orthogonal spreading code and a physical resource block (PRB)for PUCCH formats 1a/1b are obtained from n⁽¹⁾ _(PUCCH).

Hereinafter, ACK/NACK in a TDD mode will be described.

In the TDD mode, DL transmission and UL transmission are discriminatedaccording to time, such that subframes contained in a frame may beclassified into DL subframes and UL subframes. Table 3 below anexemplary UL-DL configuration in a TDD mode.

TABLE 3 Uplink- Subframe number downlink configuration 0 1 2 3 4 5 6 7 89 0 D S U U U D S U U U 1 D S U U D D S U U D 2 D S U D D D S U D D 3 DS U U U D D D D D 4 D S U U D D D D D D 5 D S U D D D D D D D 6 D S U UU D S U U D

In Table 3, D is a DL subframe, U is a UL subframe, and S is a specialsubframe. The special subframe denoted by S may include three fields,i.e., downlink pilot timeslot (DwPTS), guard period (GP), and uplinkpilot timeslot (UpPTS). DwPTS is a time period reserved for DLtransmission, and UpPTS is a time period reserved for UL transmission.

In a TDD system, a UE may transmit ACK/NACK information as a response toPDSCH transmission in one or more DL subframe in one UL subframe. The UEmay transmit HACK ACK/NACK information in a UL subframe n as a responseto transmission of PDSCH received in a DL subframe (n−k). k may be givenaccording to the UL-DL configuration. For example, k may be given as aDL related set index K: {k₀, k,₁ . . . , k_(M-1)} according to the UL-DLof Table 3 as shown in Table 4 below.

TABLE 4 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 — — 6 — 4 —— 6 — 4 1 — — 7, 6 4 — — — 7, 6 4 — 2 — — 8, 7, 4, 6 — — — — 8, 7, 4, 6— — 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 7, 11 6, 5, 4, 7 — —— — — — 5 — — 13, 12, 9, 8, 7, 5, 4, 11, 6 — — — — — — — 6 — — 7 7 5 — —7 7 —

For example, in Table 4 above, since k=4 is given in a UL subframe 9 inthe case of UL-DL configuration 0, ACK/NACK information about datareceived in a DL subframe 5 (=9-4) may be transmitted in the UL subframe9. Hereinafter, a method of determining a PUCCH resource index fortransmission of ACK/NACK in a TDD system will be described in detail.

In Table 4 above, the number of elements {k₀, k,₁ . . . k_(M-1)} of aset K is referred to as M. For example, in the case of UL-DLconfiguration 0, the number of elements of the set K for a subframe 2 is1, and in the case of UL-DL configuration 2, the number of elements ofthe set K for the subframe 2 is 4.

For TDD ACK/NACK bundling or TDD ACK/NACK multiplexing in a subframe nwith M=1, the UE may determine a PUCCH resource n⁽¹⁾ _(PUCCH) for HARQACK/NACK transmission in a subframe n as follows.

When a PDCCH indicating SPS release or PDSCH transmission indicated by aPDCCH is present in a subframe (n−k) (k∈K), the UE selects p from {0, 1,2, 3} to satisfy N_(p)≤n_(CCE)<N_(p+1). A PUCCH resource index n⁽¹⁾_(PUCCH) may be determined according to Equation 2 below.

n _(PUCCH) ⁽¹⁾=(M−m−1)×N _(p) +m×N _(p)+1+n _(CCE) +N _(PUCCH)⁽¹⁾  [Equation 2]

In Equation 2 above, n⁽¹⁾ _(PUCCH) is a resource index of PUCCH format 1for transmission of ACK/NACK, N⁽¹⁾ _(PUCCH) is a signaling valuetransmitted from a higher layer, and n_(CCE) is a smallest value amongCCE indexes used for PDCCH transmission in a subframe (n−k_(m)) (here,k_(m) is a smallest value in a set K). N_(p) may be determined accordingto Equation 3 below.

N _(p)=max{0,└[N _(RB) ^(DL)×(N _(sc) ^(RB) ×p−4)]/36┘}  [Equation 3]

In Equation 3 above, N_(RB) ^(DL) refers to DL bandwidth configurationand is represented in a unit of N_(sc) ^(RB). N_(sc) ^(RB) is a size ofa resource block in the frequency domain and is represented by thenumber of subcarriers.

When PDSCH transmission is present in a subframe (n−k) (k∈K) without aPDCCH, n⁽¹⁾ _(PUCCH) may be determined according to higher layerconfiguration.

For TDD ACK/NACK multiplexing in a subframe n with M>1, the UE maydetermine a PUCCH resource for HARQ ACK/NACK transmission as follows.Hereinafter, n⁽¹⁾ _(PUCCH) (0≤i≤M−1) is referred to as an ACK/NACKresource derived from a subframe (n−k_(i)) and HARQ-ACK(i) is referredto as ACK/NACK response from a subframe (n−k_(i)).

When a PDCCH indicating SPS release or PDSCH transmission indicated by aPDCCH is present in a subframe (n−k_(i)) (k_(i)∈K), an ACK/NACK resourcen⁽¹⁾ _(PUCCH,i) may be determined according to Equation 4 below.

n _(PUCCH,i) ⁽¹⁾=(M−i−1)×N _(p) +i×N _(p+1) +n _(CCE,i) +N _(PUCCH)⁽¹⁾  [Equation 4]

In Equation 4, N⁽¹⁾ _(PUCCH) is a signaling value transmitted from ahigher layer. n_(CCE,i) is a smallest value among CCE indexes used forPDCCH transmission in a subframe p is selected from {0, 1, 2, 3} tosatisfy N_(p)≤n_(CCE,i)<N_(p+1). Np may be determined according toEquation 3 above.

When PDSCH transmission is present in a subframe (n−k_(i)) (k_(i)∈K)without a PDCCH, n⁽¹⁾ _(PUCCH,i) may be determined according to higherlayer configuration.

The UE transmits bits b(0), b(1) on an ACK/NACK resource n⁽¹⁾ _(PUCCH)in a subframe n using PUCCH format 1b. b(0), b(1) and an ACK/NACKresource n⁽¹⁾ _(PUCCH) may be generated by channel selection accordingto Tables 5, 6, and 7 below. Tables 5, 6, and 7 show ACK/NACKmultiplexing in the cases of M=2, M=3, and M=4, respectively. Whenb(0)b(1) is mapped to N/A, the UE may not transmit ACK/NACK response ina subframe n.

TABLE 5 HARQ-ACK(0), HARQ-ACK(1) n_(PUCCH) ⁽¹⁾ b(0), b(1) ACK, ACKn_(PUCCH,1) ⁽¹⁾ 1, 1 ACK, NACK/DTX n_(PUCCH,0) ⁽¹⁾ 0, 1 NACK/DTX, ACKn_(PUCCH,1) ⁽¹⁾ 0, 0 NACK/DTX, NACK n_(PUCCH,1) ⁽¹⁾ 1, 0 NACK, DTXn_(PUCCH,0) ⁽¹⁾ 1, 0 DTX, DTX N/A N/A

TABLE 6 HARQ-ACK(0), HARQ-ACK(1), HARQ-ACK(2) n_(PUCCH) ⁽¹⁾ b(0), b(1)ACK, ACK, ACK n_(PUCCH,2) ⁽¹⁾ 1, 1 ACK, ACK, NACK/DTX n_(PUCCH,1) ⁽¹⁾ 1,1 ACK, NACK/DTX, ACK n_(PUCCH,0) ⁽¹⁾ 1, 1 ACK, NACK/DTX, NACK/DTXn_(PUCCH,0) ⁽¹⁾ 0, 1 NACK/DTX, ACK, ACK n_(PUCCH,2) ⁽¹⁾ 1, 0 NACK/DTX,ACK, NACK/DTX n_(PUCCH,1) ⁽¹⁾ 0, 0 NACK/DTX, NACK/DTX, ACK n_(PUCCH,2)⁽¹⁾ 0, 0 DTX, DTX, NACK n_(PUCCH,2) ⁽¹⁾ 0, 1 DTX, NACK, NACK/DTXn_(PUCCH,1) ⁽¹⁾ 1, 0 NACK, NACK/DTX, NACK/DTX n_(PUCCH,0) ⁽¹⁾ 1, 0 DTX,DTX, DTX N/A N/A

TABLE 7 HARQ-ACK(0), HARQ-ACK(1), HARQ-ACK(2), HARQ-ACK(3) n_(PUCCH) ⁽¹⁾b(0), b(1) ACK, ACK, ACK, ACK n_(PUCCH,1) ⁽¹⁾ 1, 1 ACK, ACK, ACK,NACK/DTX n_(PUCCH,1) ⁽¹⁾ 1, 0 NACK/DTX, NACK/DTX, NACK, DTX n_(PUCCH,2)⁽¹⁾ 1, 1 ACK, ACK, NACK/DTX, ACK n_(PUCCH,1) ⁽¹⁾ 1, 0 NACK, DTX, DTX,DTX n_(PUCCH,0) ⁽¹⁾ 1, 0 ACK, ACK, NACK/DTX, NACK/DTX n_(PUCCH,1) ⁽¹⁾ 1,0 ACK, NACK/DTX, ACK, ACK n_(PUCCH,3) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX,NACK/DTX, NACK n_(PUCCH,3) ⁽¹⁾ 1, 1 ACK, NACK/DTX, ACK, NACK/DTXn_(PUCCH,2) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, ACK n_(PUCCH,0) ⁽¹⁾ 0, 1ACK, NACK/DTX, NACK/DTX, NACK/DTX n_(PUCCH,0) ⁽¹⁾ 1, 1 NACK/DTX, ACK,ACK, ACK n_(PUCCH,3) ⁽¹⁾ 0, 1 NACK/DTX, NACK, DTX, DTX n_(PUCCH,1) ⁽¹⁾0, 0 NACK/DTX, ACK, ACK, NACK/DTX n_(PUCCH,2) ⁽¹⁾ 1, 0 NACK/DTX, ACK,NACK/DTX, ACK n_(PUCCH,3) ⁽¹⁾ 1, 0 NACK/DTX, ACK, NACK/DTX, NACK/DTXn_(PUCCH,1) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, ACK n_(PUCCH,3) ⁽¹⁾ 0, 1NACK/DTX, NACK/DTX, ACK, NACK/DTX n_(PUCCH,2) ⁽¹⁾ 0, 0 NACK/DTX,NACK/DTX, NACK/DTX, ACK n_(PUCCH,3) ⁽¹⁾ 0, 0 DTX, DTX, DTX, DTX N/A N/A

In Tables 5, 6, and 7 above, HARQ-ACK(i) indicates the HARQ ACK/NACK/DTXresult of an i-th data unit (0≤i≤3). Discontinuous transmission (DTX)represents that there is no transmission of a data unit corresponding toHARQ-ACK(i) or the UE does not detect the data unit corresponding toHARQ-ACK(i). Throughout this specification, HARQ-ACK is interchangeablyused. Maximum 4 PUCCH resources (i.e., n⁽¹⁾ _(PUCCH,0) to n⁽¹⁾_(PUCCH,3)) can be occupied for each data unit. The multiplexed ACK/NACKsignal is transmitted through one PUCCH resource selected from theoccupied PUCCH resources. In Tables 5, 6, and 7 above, n⁽¹⁾ _(PUCCH,X)represents a PUCCH resource actually used for ACK/NACK transmission, andb(0)b(1) indicates two bits transmitted through the selected PUCCHresource, which are modulated using QPSK. For example, as shown in Table7 above, when the UE has decoded 4 data units successfully, the UEtransits bits (1, 1) to a BS through a PUCCH resource linked with n⁽¹⁾_(PUCCH,1). Since combinations of PUCCH resources and QPSK symbolscannot represent all available ACK/NACK suppositions, NACK and DTX arecoupled except some cases (NACK/DTX, N/D).

Enhanced-Control Channel Based Operation

The present invention proposes a method using a scrambling sequenceparameter and/or a plurality of antenna ports associated with anenhanced control channel (e.g., an E-PDCCH).

First, to aid in understanding of the present invention, a method ofdetermining one or more PUCCH resources for transmission of ACK/NACK toDL data scheduled via the E-PDCCH using the scrambling sequenceparameter and/or the plural antenna ports associated with an E-PDCCHwill be described.

Method of Determining PUCCH Resource Associated with E-PDCCH

The UE may detect a control channel containing information (or DLscheduling information) about DL assignment and receive a PDSCHcorresponding to the control channel. The UE may feedback informationabout whether PDSCH reception is successful after a predetermined periodof time. In a 3GPP LTE system, a resource to be used for ACK/NACKtransmission may be determined from a PDCCH in which the DL assignmentis transmitted. As described above, the UE may recognize a first index(e.g., an index n) from CCEs of a PDCCH used for transmission of DLassignment and transmit ACK/NACK using a PUCCH resource corresponding toN_(offset) ^(PUCCH)+n obtained by adding the CCE index to N_(offset)^(PUCCH) as offset indicating beginning of a PUCCH resource region usedfor ACK/NACK. Here, N_(offset) ^(PUCCH) may be a value signaled by ahigher layer like N⁽¹⁾ _(PUCCH) of Equation 1 above.

The method of determining a PUCCH resource based on a CCE index of aPDCCH can be applied to the legacy-PDCCH in which one CCE is used foronly one UE without any problem, but it can be difficult to apply themethod to an enhanced PDCCH (i.e., an E-PDCCH). Unlike the legacy-PDCCH,the E-PDCCH can be demodulated based on a UE-specific RS (or DMRS) andcan apply MU-MIMO. Accordingly, when a PUCCH resource is determinedusing a conventional method, ACK/NACK resource collision may occur. Forexample, when MU-MIMO is applied to the E-PDCCH, two or more UEs canreceive DL assignment divided according to precoding (or UE-specific RS(or DMRS)) while sharing the same time/frequency resource (i.e., CCE orECCE, and hereinafter, referred to as (E)CCE). In this case, when theconventional PUCCH resource determination method is still used, aplurality of UEs (i.e., UEs belonging to one E-PDCCH MU-MIMO group)using the same (E)CCE can simultaneously transmit ACK/NACK signals usingthe same PUCCH resource (i.e., ACK/NACK resource collision).

To address this issue, according to the present invention, when DLassignment is received using an E-PDCCH, a plurality of PUCCH resourcesfor one DL assignment is reserved as ACK/NACK resources, and anindividual UE selects some of the plural reserved PUCCH resources andperforms ACK/NACK feedback.

For example, when DL assignment is received using an aggregation level L(i.e., using (E)CCE n₀, n₁, . . . , n_((L-1))), a UE may select one ofthe L PUCCH resources linked with the L (E)CCEs and feedback ACK/NACK.

In this case, a PUCCH resource to be used by each UE may be determinedbased on a parameter k (k=0, 1, 2, 3, . . . ). A value of the parameterk may be indicated using a specific field in DL assignment or selectedfrom the feature of an RS (UE-specific RS or DMRS) used for detection(or demodulation) of DL assignment.

For example, when the specific field in DL assignment indicates k, aPUCCH resource linked with (E)CCE having an index corresponding to k canbe selected.

Hereinafter, an example in which a PUCCH resource is selected from thefeature of an RS associated with an E-PDCCH will be described in detail.

For example, when an antenna port number of a UE-specific RS (or DMRS)used for demodulation of a PDCCH for carrying DL assignment is p (e.g.,p∈{7, 8, 9, 10} or p∈{107, 108, 109, 110}), a PUCCH resource linked with(E)CCE n_(k) may be selected. Here, a relationship between k and p maybe given by k=(p−7) mod L (p∈{7, 8, 9, 10}) or k=(p−107) mod L (p∈{107,108, 109, 110})). Here, k is an (E)CCE index number, p is an antennaport number, and L is an aggregation level. In addition, mod refers tomodulo calculation and X mod Y refers to a remainder obtained bydividing X by Y. For example, with regard to L=2, when an antenna portnumber 7 or 9 (or an antenna port number 107 or 109) is used, a PUCCHresource linked with (E)CCE n₀ may be selected, and when an antenna portnumber 8 or 10 (or antenna port number 108 or 110) is used, a PUCCHresource linked with (E)CCE n1 may be selected.

An (E)CCE index may be selected using a scramble sequence initializationvalue of a UE-specific RS (or DMRS) used for demodulation of a PDCCH forcarrying DL assignment and an ACK/NACK resource linked with the selected(E)CCE index. The scramble sequence initialization value may be referredto as a scrambling identifier (SCID).

For example, according to a combination of an antenna port number and anSCID, a resource to be used as ACK/NACK feedback may be determined. Forexample, the form such as k=((p−7)+(SCID)) mod L or k=((p−107)+(SCID))mod L may be given.

As described above, according to a method for determining an ACK/NACKresource using a scrambling sequence parameter and/or a plurality ofantenna ports associated with an E-PDCCH, in order to determine PUCCHthat does not collide with each UE that belongs to the same E-PDCCHMU-MIMO group, an eNB needs to be appropriately configure an E-PDCCHaggregation level, an (E)CCE index number, an antenna port of an RS(UE-specific RS or DMRS), and/or a scrambling sequence and to transmitan E-PDCCH for each UE.

Here, the above proposed operation can be smoothly performed when one DLassignment has a plurality of (E)CCEs, the operation may be limited toonly a case of two or more aggregation levels. This means that two ormore aggregation levels need to be used in order to transmit DLassignment using MU-MIMO by an eNB.

For another example, when DL assignment is received using an aggregationlevel L (i.e., using (E)CCE n₀, n₁, . . . , n_((L-1))), the UE maydetermine a specific (E)CCE index n* (e.g., (E)CCE n₀ with a lowestindex or (E)CCE index derived from a UE ID, etc.) among the L (E)CCEs,select a PUCCH resource (e.g., n*+k+N_(offset) ^(PUCCH)) linked with an(E)CCE index n*+k obtained by applying predetermined offset (e.g., k) tothe specific (E)CCE index (which means an index corresponding to arepresentative AP of an E-PDCCH according to one-to-one correspondence),and feedback ACK/NACK.

Here, a parameter k corresponding to offset may be indicated using aspecific field of a DCI format of DL assignment like in theaforementioned example or determined by a scramble sequenceinitialization value (e.g., SCID) and/or an antenna port of an RS usedfor demodulation of DL assignment. A DCI format of DL assignment mayrefer to, for example, a DCI format 1A, 1B, 1D, 1, 2A, 2, 2B, 2C, 2D,etc.

For example, when a UE can use a PUCCH resources linked with (E)CCEsexcept for an aggregated (E)CCE, the offset k may be determined in theform of k=(p−7) or k=((p−7)+(SCID)) (in this case, it is assumed thatthe UE uses an antenna port p and p∈{7, 8, 9, 10}). This method may beuseful for transmission of MU-MIMO E-PDCCH particularly when anaggregation level is 1 (i.e., when only one (E)CCE is used).

k may be determined as follows. For example, it is assumed that the UEmay use a PUCCH resource linked with an (E)CCE positioned before n₀corresponding to a first (or lowest) (E)CCE index used in correspondingDL assignment on an (E)CCE index. In this case, the UE may use a PUCCHresource N_(offset) ^(PUCCH)+n₀+k and k=(7−p) may be given. For example,in the case of an antenna port 7, a PUCCH resource N_(offset)^(PUCCH)+n₀ and may be used, in the case of an antenna port 8, a PUCCHresource N_(offset) ^(PUCCH)+n₀−1 may be used.

For another example, an ACK/NACK PUCCH resource region is divided into Kregions, a start point of each region k(=0, 1, . . . , K−1) is indicatedto the UE in the form of N_(offset) ^(PUCCH)(k), and then the UE maydetermine a specific (E)CCE index n* (e.g., (E)CCE n₀ with a lowestindex or an (E)CCE index derived from a UE ID, etc.) associated withtransmission of DL assignment, select an appropriate PUCCH resourceregion k, and use a PUCCH resource N_(offset) ^(PUCCH)(k)+n*.

Here, a parameter k corresponding to an index of a PUCCH region may beindicated using a specific field of a DCI format of DL assignment likein the aforementioned example or determined by a scramble sequenceinitialization value (e.g., SCID) and/or an antenna port of an RS usedfor demodulation of DL assignment.

For another example, a plurality of PUCCH resources may be linked withone (E)CCE. When one (E)CCE is linked with K PUCCH resources, the UE maydetermine a specific (E)CCE index n* (e.g., (E)CCE n₀ with a lowestindex or an (E)CCE index derived from a UE ID, etc.) associated withtransmission of DL assignment, select an appropriate k, and use a PUCCHresource N_(offset) ^(PUCCH)+Kn*+k.

Here, a parameter k associated with determination of a PUCCH resourceindex may be indicated using a specific field of a DCI format ofassignment like in the aforementioned example or may be determined by ascramble sequence initialization value (e.g., SCID) and/or an antennaport of an RS used for demodulation of DL assignment.

In the aforementioned examples, a PUCCH resource region may beclassified (divided) into a region used when a legacy-PDCCH receives DLassignment and a region used when an E-PDCCH receives DL assignment. Inparticular, the classification (or division) is effective to preventACK/NACK resource collision of a legacy-PDCCH and a PDSCH scheduled byan E-PDCCH. In this case, an eNB needs to divide an offset valueN_(offset) ^(PUCCH) indicating a start point of each PUCCH resourceregion into values for the legacy-PDCCH and the E-PDCCH and to indicatethe values.

The methods according to the present invention can be restrictedlyapplied to a specific E-PDCCH search space (e.g., a UE-specific searchspace). This is because DCI that is simultaneously received by many UEsis generally transmitted in a common search space, and thus, thenecessity of using MU-MIMO is low.

The methods according to the present invention can be restrictedlyapplied only to E-PDCCH transmission of a specific transmission modeappropriate for application of MU-MIMO. For example, in order to achievediversity in a frequency domain or a space domain similarly to a legacyPDCCH, an E-PDCCH may be divided into a plurality of REGs, and aninterleaved E-PDCCH transmission mode (e.g., a distributed type E-PDCCHtransmission) for interleaving the REGs can be defined, or anon-interleaved E-PDCCH transmission mode (e.g., localized type E-PDCCHtransmission) in which one E-PDCCH (E)CCE is transmitted only in onefrequency domain unit (e.g., a PRB pair) or one space domain unit can bedefined. In this regard, the aforementioned method of determining aPUCCH resource using the scrambling sequence parameter and/or theantenna port associated with the E-PDCCH may not be applied in theinterleaved E-PDCCH transmission mode in which it is difficult to applyMU-MIMO and may be applied only to a non-interleaving transmission modein which application of MU-MIMO is appropriate.

The methods according to the present invention can be restrictedlyapplied to a specific aggregation level. For example, an E-PDCCH usingmany (E)CCEs like in the case of an aggregation level 4 or 8 isgenerally used when a channel status is poor, and thus, it may not beappropriate to apply MU-MIMO. Accordingly, the aforementioned method ofdetermining a PUCCH resource using the scrambling sequence parameterand/or the antenna port associated with the E-PDCCH may restrictedlyapplied to a low aggregation level such as an aggregation level 1 or 2.

Likewise, in order to appropriately select a method of determining anACK/NACK PUCCH resource according to a condition, the eNB may notify theUE of how an ACK/NACK feedback resource is used for each respectivesearch space or subframe via a higher layer signal such as an RRC. Inaddition, when a plurality of PUCCH resource regions is used or aplurality of PUCCH resources is linked with one (E)CCE, the eNB maynotify the UE of information about the number of the PUCCH resourceregions or information about the number of the PUCCH resources linkedwith one (E)CCE via a higher layer signal such as a RRC.

In addition, as another method for preventing the aforementionedACK/NACK resource collision, separate PUCCH resources other than a PUCCHresource linked with (E)CCE may be reserved using a higher layer signalsuch as an RRC, and an appropriate resource may be selected amongseparate PUCCH resources. For example, a UE that decodes DL assignmentmay recognize one PUCCH resource linked with (E)CCE, also recognize somePUCCH resources pre-transmitted via an RRC, and then determine a finalPUCCH resource to be used for ACK/NACK transmission via appropriateindication. Here, indication for determination of a resource used foractual transmission among the PUCCH resources recognized by the UE maybe determined using a specific field in DL assignment or determined froma scramble sequence initialization value (e.g., SCID) and/or an antennaport of an RS used for detection (or demodulation) of DL assignment.

For example, it is assumed that the UE recognizes one PUCCH resource(e.g., a PUCCH resource n₁) linked with (E)CCE used for transmission ofDL assignment and recognizes three PUCCH resources (e.g., PUCCHresources n₂, n₃, and n₄) pre-configured via an RRC.

In this case, when a specific field value in DL assignment is given byone of 00, 01, 10, and 11, one of PUCCH resources n1, n2, n3, and n4 maybe determined.

In addition, when an RS associated with an E-PDCCH is one of antennaport numbers 7, 8, 9, and 10 (or 107, 108, 109, and 110), one of thePUCCH resources n1, n2, n3, and n4 may be determined.

In the aforementioned examples, to aid in understanding of principle ofthe present invention, the case in which the UE performs ACK/NACKfeedback using one PUCCH resource has been described, but the scope ofthe present invention is not limited thereto. For example, when a UE forsupporting transmission of multi-antenna port uses a plurality of PUCCHresources in order to obtain transmit diversity, etc., a PUCCH resourcemay also be appropriately determined in order to prevent PUCCH resourcecollision according to the aforementioned principle of the presentinvention. For example, when one UE uses two PUCCH resources, a firstPUCCH resource may be determined as n* and a second PUCCH resource maybe determined as n*+1 according to the aforementioned method.

Hereinafter, examples in which one UE transmits ACK/NACK using aplurality of PUCCH resources in order to obtain transmit diversity willbe described in detail.

In the following examples, it may be assumed that the UE detects (ordemodulates) an E-PDCCH using one antenna port of an RS and a pluralityof PUCCH resources to be used for transmit diversity may be indicted byone antenna port.

Like in the example in which the UE detects a plurality of (E)CCEs of anE-PDCCH using different antenna ports, when the E-PDCCH is detectedusing the plural antenna ports, the UE may determine a PUCCH resourceusing one representative antenna port (or a virtual antenna port). Therepresentative antenna port may be determined as an antenna port with aminimum index among the used antenna ports or determined as the antennaport used to detect a representative (E)CCE (e.g., (E)CCE with a minimumindex).

For example, when DL assignment is received using an aggregation level L(i.e., (E)CCE n₀, n₁, . . . , n_((L-1))), a UE may select M resourcesamong the L PUCCH resources linked with the L (E)CCEs and feedbackACK/NACK.

When an antenna port number of a UE-specific RS (or DMRS) used fordemodulation of a PDCCH for carrying DL assignment is p (e.g., p∈{7, 8,9, 10} or p∈{107, 108, 109, 110}), a PUCCH resource linked with two(E)CCEs n_(k) and n_((k+1)) may be selected. Here, a relationshipbetween k and p may be given in the form of k=(p−7)*M mod L or may begiven by k=(p−107)*M mod L.

When M=2 and L=4 are given, if an antenna port associated with detectionof E-PDCCH is 7 or 9 (or if the antenna port is 107 or 109), the UE mayselect PUCCH resources n₀ and n₁, and if the antenna port is 8 or 10 (orif the antenna port is 108 or 110), the UE may select PUCCH resources n₂and n₃.

When PUCCH resources linked with (E)CCEs that do not belong to the sameE-PDCCH can be used, k=(p−7)*M (or k=(p−107)*M) may be determined, andif k<L−1, n_(k)=n_((L-1))+k−L+1 may be determined.

In the aforementioned examples, the case in which k is determined basedon an antenna port number has been described. However, k may bedetermined based on a scramble sequence initialization value (e.g.,SCID) of an RS associated with an E-PDCCH.

For another example, an ACK/NACK PUCCH resource region is divided into Kregions, a start point of each region k(=0, 1, . . . , K−1) is indicatedto the UE in the form of N_(offset) ^(PUCCH)(k), and then the UE maydetermine a specific (E)CCE index n* (e.g., (E)CCE n₀ with a lowestindex or an (E)CCE index derived from a UE ID, etc.) associated withtransmission of DL assignment and use M appropriate PUCCH resourcesN_(offset) ^(PUCCH)(k)+n*, N_(offset) ^(PUCCH)(k+1)+n*, . . . ,N_(offset) ^(PUCCH) (k+M−1)+n*. Here, as an example of determination ofk, k may be given in the form of k=(p−7)*M (or k=(p−107)*M). Inaddition, K that is the number of PUCCH resource regions may beassociated with an ACK/NACK transmission method in a PUCCH. For example,when a PUCCH transmission diversity mode with M=2 is set, since doubledPUCCH resources are required compared with M=1 in general, K may be setto be twice as high as in the case of M=1. Accordingly, the UE maychange the number of regions obtained by dividing ACK/NACK PUCCHresource regions based on an ACK/NACK transmission method in a PUCCHresource.

In addition, a plurality of PUCCH resources may be linked with one(E)CCE. When one (E)CCE uses K PUCCH resources, the UE may determine aspecific (E)CCE index n* (e.g., (E)CCE n₀ with a lowest index or (E)CCEindex derived from a UE ID, etc.) associated with transmission of DLassignment and use M PUCCH resources N_(offset) ^(PUCCH)+Kn*+k,N_(offset) ^(PUCCH)+Kn*+k+1, . . . , N_(offset) ^(PUCCH)+Kn+k+M−1. Here,as an example of determination of k, k may be given in the form ofk=(p−7)*M (or k=(p−107)*M). In addition, K that is the number of PUCCHresource regions may be associated with an ACK/NACK transmission methodin a PUCCH. For example, when a PUCCH transmission diversity mode withM=2 is set, since doubled PUCCH resources are required compared with M=1in general, K may be set to be twice as high as in the case of M=1.

Like in the aforementioned examples, when ACK/NACK transmission isperformed using a plurality of PUCCH resources, the number of UEs thatsimultaneously belong to one MU-MIMO group in one E-PDCCH resource maybe limited.

For example, it may be assumed that four PUCCH resources m₀, m₁, m₂, andm₃ are allocated to one E-PDCCH resource. In detail, a single E-PDCCHresource includes four (E)CCEs and one PUCCH resource is linked witheach respective (E)CCE, or a single E-PDCCH resource includes two(E)CCEs and two PUCCH resources are linked with each (E)CCE. In thiscase, the present invention may be limited to a case in which MU-MIMO isperformed on up to two UEs that perform transmit diversity using twoPUCCH resources. Here, in the case of a UE to which PUCCH transmitdiversity is applied, when an antenna port 7 (or 107) is used inrelation to an E-PDCCH, PUCCH resources m₀ and m₁ may be used, and whenan antenna port 8 (or 108) is used in relation to an E-PDCCH, PUCCHresources m₂ and m₃ may be used. MU-MIMO may be performed on up to fourUEs to which PUCCH transmit diversity is applied. In this case, each UEmay occupy one PUCCH resource. Here, in order to use the same PUCCHresource if possible in both cases in which PUCCH transmit diversity isapplied and is not applied, a UE to which PUCCH transmission diversityis not applied may use PUCCH resources m₀, m₂, m₁, and m₃, respectivelywhen the UE uses antenna ports 7, 8, 9, and 10 (or 107, 108, 109, and110) in relation to an E-PDCCH.

Method of Determining Representative Antenna Port

Hereinafter, an E-PDCCH related operation using a representative antennaport (or a virtual antenna port) will be described with regard toembodiments of the present invention.

As described above, when one E-PDCCH is transmitted using a plurality ofresource regions (e.g., (E)CCE), different antenna ports may be mappedto respective resource regions. In this case, one representative antennaport may be determined and the E-PDCCH related operation may beperformed based on the representative antenna port.

The representative antenna port may be determined according to any oneof the following methods.

Method 1—The representative antenna port may be determined to have aminimum index among antenna port(s) mapped to an E-PDCCH resourceregion. For example, when an antenna port 7 (or 107) is mapped in aresource region 1 and an antenna port 8 (or 108) is mapped in a resourceregion 2, the representative antenna port may be determined as theantenna port 7 (or 107) with respect to an E-PDCCH using both the tworesource regions.

Method 2—The representative antenna port may be determined to have amaximum index among antenna port(s) mapped to an E-PDCCH resourceregion. For example, when an antenna port 7 (or 107) is mapped in aresource region 1 and an antenna port 8 (or 108) is mapped in a resourceregion 2, the representative antenna port may be determined as theantenna port 8 (or 108) with respect to an E-PDCCH using both the tworesource regions.

The method 2 may be useful to prevent collision between an RS antennaport of an E-PDCCH of a cell and an RS antenna port of a PDSCH of anadjacent cell. For example, an RS that uses a PDSCH of an adjacent celluses antenna ports, the number of which corresponds to the number ofranks from the antenna port 7 as a start antenna port, according toranks of the antenna ports, and thus, an antenna port with a low indexis used more frequently. Accordingly, according to the method 2, whenthe representative antenna port of the E-PDCCH is determined, since anantenna port with a high index is more frequently used as therepresentative antenna port of the E-PDCCH, a collisional frequency withthe antenna port of the PDSCH of the adjacent cell can be reduced. Inaddition, the method 2 is particularly effective to E-PDCCH demodulationusing the representative antenna port, which will be described below.

Method 3—Priority for selection of the representative antenna port maybe pre-transmitted to the UE via a higher layer signal such as an RRC,and one of E-PDCCH related antenna port(s) may be selected according tothe priority. For example, the eNB may determine priorities for antennaports 7, 8, 9, and 10 (or antenna ports 107, 108, 109, and 110) anddetermine an antenna port with highest priority as the representativeantenna port among a plurality of antenna ports when the plural antennaports are mapped to one E-PDCCH. The method 3 is advantageous in thatthe eNB can adjust a method of determining a representative antenna portsuch that representative antenna ports between cells do not overlap witheach other (i.e., different representative antenna ports are different).

Method 4—A method of determining a representative antenna port (orpriority for selection of the representative antenna port) may bedetermined based on an (E)CCE index, an antenna port (AP) index, a UEID, a cell ID, etc. For example, a hash function may be predefined basedon parameters such as an (E)CCE index, an AP index, a UE ID, a cell ID,etc., a hash function value (i.e., a result value of the hash function)may be determined as the representative antenna port. Accordingly,without separate network signaling, different UEs may use differentrepresentative antenna ports to prevent RS collision and use a PUCCHregion divided for the respective representative antenna ports withoutcollision.

Method 5—An antenna port used to detect a representative resource region(e.g., one (E)CCE) may be determined as a representative antenna portamong resource region(s) of the E-PDCCH. Here, the representativeresource region may be a resource region with a minimum or maximum indexamong resources regions used for the E-PDCCH.

Method 6—When an antenna port used to detect a representative resourceregion is determined as a representative antenna port among resourceregion(s) of the E-PDCCH, the representative resource region may bedetermined as a resource region with a minimum resource region index.Here, the minimum resource region index may be a minimum value amongindexes present when the resource regions included in the correspondingE-PDCCH are determined (i.e., during an aggregation procedure), but nota minimum value of indexes that are finally determined for resourceregions included in the corresponding E-PDCCH. That is, a resourceregion in which aggregation begins may be determined as therepresentative antenna port.

As an example of the method 6, it may be assumed that, when a pluralityof resource regions (e.g., (E)CCE) is defined in one PRB pair andresource regions included in one E-PDCCH are limited to the same PRBpair, k contiguous resource regions from a resource region n as a startpoint may be aggregated and one E-PDCCH is transmitted. Here, theresource region n that is a resource region in which aggregation ofregions of the corresponding E-PDCCH begins (i.e., a resource regionwith a minimum index during an aggregation procedure) may be arepresentative resource region. A final index that is actually occupiedby each of the aggregated resource regions may be different from anindex of a resource region during the aggregation procedure, and thus,the minimum index and the final index needs to be differentiated duringthe aggregation procedure. For example, in k (i.e., n, n+1, n+2, n+k−1)contiguous resource regions from the resource region n as a start point,resource regions n+1, n+2, n+k−1 may be present on a different PRB froma PRB pair in which the resource region n is present. In this case, inconsideration of a condition in which resource regions included in oneE−PDCCH are limited to the same PRB pair, resource regions n, n+1−P,n+2−P, n+k−1−P (here, P is given such that resource regions n+1−P,n+2−P, n+k−1−P are present in the same PRB pair as the PRB pair in whichthe resource region n is present) may be aggregated to constitute oneE-PDCCH. In this case, even if the resource region n does not have aminimum index in a finally denoted resource region index, the resourceregion n may be determined as a resource region with a minimum indexfrom a viewpoint of the aggregation procedure, and accordingly, theresource region n may be determined as the representative resourceregion.

As another example of the method 6, it may be assumed that one PRB pairis divided into P resource regions and resource regions Pt, Pt+1, Pt+P−1are defined in a t^(th) (t=0, 1, . . . ) PRB pair. For example, whenP=3, resource regions 0, 1, and 2 may be defined in a 0^(th) PRB pair,resource regions 3, 4, and 5 may be defined in a first PRB pair, andresource regions 6, 7, and 8 may be defined in a second PRB pair. Inthis case, when resource regions Pt+P−1 and Pt+P are aggregated, aresource region index Pt+X may be substituted with an index as a resultobtained by performing calculation Pt+(X mod P) in order to prevent tworesource regions from being positioned in different PRB pairs. In theaforementioned example, a resource region Pt+P may be substituted withPt as a result of Pt+(P mod P). That is, resources regions Pt+P−1 and Ptthat belong to the same PRB may be aggregated. Here, the resource regionPt+P−1 with a minimum original index may be a representative resourceregion among aggregated resource regions. Overview of calculation of afinal resource region index will now be described. When adjacentresource regions are aggregated using a resource region Pt+n as a startpoint, resource regions Pt+((n+k) mod P (k=0, 1, . . . ) may beaggregated, and a resource region Pt+n with a minimum original index maybe determined as a representative resource region.

Method 7—An antenna port used to detect a representative resource region(e.g., (E)CCE) may be determined as a representative antenna port, andin this regard, when information about the representative resourceregion may be pre-transmitted via a higher layer signal such as an RRCor priorities between resource regions may be predetermined and aplurality of resource regions is used, a resource region with highestpriority may be determined as the representative resource region.Alternatively, when a plurality of resource regions is aggregated toconstitute one E-PDCCH, priority may be determined according to acandidate with a lower aggregation level is configured in each resourceregion. For example, one E-PDCCH and resource regions 1 and 2 areaggregated and are transmitted with an aggregation level 2, since acandidate of an aggregation level 1 using the resource region 1 ispresent, the UE attempts to detect an E-PDCCH in a correspondingresource region. On the other hand, since the candidate of theaggregation level 1 is not present in the resource region 2, if the UEdoes not attempts to detect the E-PDCCH, the resource region 1 may bedetermined as the representative resource region in order to reusechannel estimation.

In the methods 1 to 7, even if one E-PDCCH is transmitted using aplurality of resource regions (e.g., (E)CCE), different scramblingsequence parameters (e.g., SCIDs) may be mapped to respective resourceregions, a representative SCID parameter may be determined based on anindex of the SCID using the methods 1 to 3, or the representativeresource region may be determined based on the index of the resourceregion and the SCID mapped to the representative resource region may bedetermined as a representative SCID parameter.

Hereinafter, an example of a method using a representative antenna portdetermined using one of the aforementioned methods will be described.

From a viewpoint of an eNB, one representative antenna port may be usedto map an E-PDCCH to a resource element. From a viewpoint of a UE, anantenna port of an RS to be used for demodulation of the E-PDCCH may bedetermined as the representative antenna port. In this regard, therepresentative antenna port may be determined using one or more methodsamong the methods 1 to 7. This method may be effective to a case inwhich a plurality of resource regions used for one E-PDCCH is positionedin one PRB pair or in adjacent PRB pairs. This is because a channelstatus is maintained in one PRB pair or adjacent PRB pairs, and thus,individual resource regions cannot be channel-estimated using a separateRS and one channel estimation can be performed using an RS of onerepresentative antenna port. Accordingly, transmission power of an RSthat is not an RS of a representative antenna port, may be allocated toan RS of the representative antenna port to enable power boosting,thereby achieving more accurate channel estimation.

FIGS. 6 and 7 are diagrams for explanation of an operation ofdemodulating an E-PDCCH transmitted through a plurality of resourceregions using a representative antenna port according to an embodimentof the present invention. FIG. 6 illustrates a case of one PRB pair andFIG. 7 illustrates a case of adjacent PRB pairs.

In the example of FIG. 6, it is assumed that one PRB pair is dividedinto four (E)CCEs and antenna ports 7, 8, 9, and 10 are mapped torespective (E)CCEs. FIG. 6 illustrates the example in which an eNB uses(aggregates) (E)CCE 0 and (E)CCE 2 and transmits a single E-PDCCH to aUE. In this case, the UE may determine a representative antenna port oftwo resource regions (i.e., (E)CCEs 0 and 2) according to one or moremethods of the aforementioned methods. For example, it is assumed thatAP 9 (or AP 109) is selected as the representative antenna port.Accordingly, a channel can be estimated using an RS (UE-specific RS orDMRS) corresponding to the representative antenna port in the two(E)CCEs, and E-PDCCH demodulation can be used based on the estimatedchannel.

FIG. 7 illustrates the example in which two resource regions (i.e.,(E)CCEs 0 and 6) positioned in adjacent PRB pairs are aggregated and oneE-PDCCH is transmitted. In the example of FIG. 7, when therepresentative antenna port is determined as AP 9 (or AP 109), the UEmay estimate an RS corresponding to the representative antenna port andperform E-PDCCH demodulation based on the estimated channel.

One or more of the methods 1 to 9 of determination of a representativeantenna port may be complexly used.

For example, like in the method 5 or 6, the representative antenna portmay be determined as an antenna port used to detect the representativeresource region (e.g., a resource region with a minimum index). The usedmethod is advantageous in that the method can be used together withvarious operations for defining a representative resource regionassociated with resource regions, for example, an operation forselecting an ACK/NACK resource connected to a resource region. Inaddition, like in the method 3, 4, or 7, the method is advantageous inthat antenna ports between cells do not overlap each other to preventinterference between RSs when priority for determining therepresentative antenna port is determined via a higher layer signal suchas an RRC, etc. In order to provide these advantages it may be complexlyapply the aforementioned methods. In this regard, for example, therepresentative antenna port may be determined as an antenna portallocated to a representative resource region with a minimum index. Inthis regard, an index of each resource region may be determined via ahigher layer signal such as an RRC, etc.

FIG. 8 is a diagram for explanation of an operation of demodulating anE-PDCCH transmitted through a plurality of resource regions using arepresentative antenna port according to another embodiment of thepresent invention. FIG. 8 illustrates the example in which two adjacentcells allocate antenna ports to resource regions (e.g., (E)CCE) presentin the same PRB pair using the same method and denotes resource regionindexes (e.g., (E)CCE indexes) using different methods. Accordingly,even if all resource regions of the corresponding PRB pair areaggregated, representative resource regions (e.g., resource region witha minimum index in each cell) and representative antenna ports mapped tothe respective representative resource regions may be determined not tooverlap (or to be different) between cells.

In the example of FIG. 8, since a cell 1 and a cell 2 denote indexes forresource regions using different methods, even if the indexes (i.e.,lowest index) of representative resource regions are the same value, 0,positions of physical resource regions that are actually indicated bythe respective resource region indexes may be differently determined,and thus, different representative resource regions may be determinedfor the respective cells. Accordingly, antenna ports (i.e.,representative antenna ports) mapped to the determined representativeresource regions may also be differently determined.

In the example of FIG. 8, a UE that belongs to the cell 1 may determinea resource region (a first resource region from a viewpoint of aphysical resource position) corresponding to a resource region index 0as a representative resource region, determine an antenna port (i.e., AP7) corresponding to the determined representative resource region as arepresentative antenna port, and demodulate all resource regions(resource region indexes 0 to 3) of one E-PDCCH using an RScorresponding to the representative antenna port. A UE that belong tothe cell 2 may determine a resource region (a third resource region froma viewpoint of a physical resource position) corresponding to a resourceregion index 0 as representative resource region, determine an antennaport (i.e., AP 9) corresponding to the determined representativeresource region as the representative antenna port, and demodulate allresource regions (resource region indexes 0 to 3) of one E-PDCCH usingan RS corresponding to the representative antenna port.

According to a method of denote an index for a resource region, an indexfor each resource region may be denoted directly via a higher layersignal such as an RRC or derived from parameters such as a cell ID, a UEID, etc. according to a predetermined rule.

For example, the eNB may transmit a specific seed value to the UE viadirect signaling or indirect signaling derived from other parameters.The UE may denote predetermined offset to an index of an E-PDCCHresource region (e.g., (E)CCE) based on the corresponding seed valuetransmitted from the eNB or correct (e.g., permutation, cyclic shift, orinterleaving) a position of a resource region index to a patterndetermined according to the corresponding seed value.

In the example of FIG. 8, when the cell 2 denotes an index to a resourceregion, offset corresponding to 2 is applied compared with an indexdenoted by the cell 1.

For inter-cell interference coordination (ICIC), a specific cell maytransmit information about a method of denoting a resource region indexby the cell and information about a standard (e.g., priority for eachantenna port applied for determination of a representative antenna port,information about an antenna port allocated to each resource region,etc.) applied for determination of an antenna port to adjacent cells viabackhaul, etc.

The aforementioned operation of determining the representative resourceregion and/or the operation of determining the representative antennaport can be applied to all E-PDCCH PRB pairs, can be applied in units ofseparate PRB pairs, or can be applied in units of PRB pair groups (e.g.,a set of a predetermined number of adjacent PRB pairs). In particular,when channel estimation is performed in units of PRB pairs or in unitsof PRB pair groups, one representative antenna port may be selected froma PRB pair or a PRB pair group, and resource regions that belong to thesame PRB pair or PRB pair group may be attempted to be detected as acorresponding representative antenna port among resource regionsaggregated with a specific E-PDCCH (or demodulation of an E-PDCCH may beattempted using an RS corresponding to the corresponding representativeantenna port).

Hereinafter, the aforementioned operation of determining arepresentative antenna port will be described with regard to anembodiment of the present invention in detail. As a representativeexample of the present invention, it is assumed that the method 4 isused among the aforementioned methods. That is, a detailed example of amethod of defining a hash function based on other parameters such as an(E)CCE index, a port index, a UE ID, and a cell ID and determining avalue of the function as a representative antenna port will bedescribed.

When an aggregation level of an E-PDCCH is L, this means that oneE-PDCCH includes an aggregation of L (E)CCEs. The L (E)CCEs may berepresented by #n_(CCE), #n_(CCE)+1, #n_(CCE)+2, #n_(CCE)+L−1 (or#n_(ECCE), #n_(ECCE)+1, #n_(ECCE)+2, #n_(ECCE)+L−1). An index of anantenna port (AP) allocated (or mapped) to each (E)CCE may be determinedas follows.

Example 1—Four (E)CCEs may be formed in one PRB pair, and APs #p, #p+1,#p+2, and #p+3 may be sequentially allocated in an order of the (E)CCEs.The example can be applied to a case in which four or more APs aredefined like a normal CP subframe and the number of REs that can be usedas an E-PDCCH is also sufficient.

Example 2—Two (E)CCEs may be formed in one PRB pair, and APs #p and #p+2may be sequentially allocated in an order of the (E)CCEs. The examplecan be applied to a case in which four or more APs are defined like anormal CP subframe but the number of REs that can be used as an E-PDCCHis not sufficient and thus only two (E)CCEs are formed in one PRB pair.

In this case, since DMRSs (i.e., DMRS ports #p and #p+2), which arepositioned away from each other by as much as 2 in an AP index, areused, the DMRSs may be transmitted to be independently consumed indifferent REs. For example, DMRS ports 7 and 8 (or 107 and 108) may bemultiplexed and transmitted using a CDM method via different orthogonalcover codes in the same RE, and DMRS ports 9 and 10 (or 109 and 110) maybe multiplexed and transmitted using a CDM method via differentorthogonal cover codes in other the same RE. Liked in the aforementionedexample 2, when APs 7 and 9 (or APs 107 and 109) are allocated to two(E)CCEs, since positions of REs for transmission of a DMRS of APs 7 and9 (or 107 and 109) are different, respective values of RE transmissionpower can be applied to the APs.

Example 3—Two (E)CCEs may be formed in one PRB pair, and APs #p and #p+1may be sequentially allocated in an order of the (E)CCEs. The examplecan be applied to a case in which only two APs are defined like anextended CP subframe.

Here, a representative AP index for the E-PDCCH may be determinedaccording to a function (e.g., a hash function) of Equation 5 below.

A=p+{(n _(CCE) mod d)+(X mod L)}*Z or

AP−p+{(n _(ECCE) mod d)+(X mod L)}*Z  [Equation 5]

In addition, a representative AP index may be determined according to afunction of Equation 6 below. Equation 6 below may be defined to limitselection of one of d AP indexes as a representative AP index when anaggregation level of an E-PDCCH exceeds the number of (E)CCEs formed onone PRB pair, d.

AP=p+{(n _(CCE) mod d)+(X mod min(L,d))}*Z, or

AP=p+{(n _(ECCE) mod d)+(X mod min(L,d))}*Z

In Equations 5 and 6 above, p refers to a minimum value (i.e., 7 or 107)of a DMRS port index (a port index 7, 8, 9, or 10, or a port index 107,108 109, or 110) used by an E-PDCCH. n_(CCE) or n_(ECCE) refers to alowest value among indexes of (E)CCE used for E-PDCCH transmission(e.g., which may be represented by n_(CCE,low) or n_(ECCE,low)). Drefers to the number of (E)CCEs formed on one PRB pair (e.g., which maybe represented by N_(RB) ^(CCE) or N_(RB) ^(ECCE)). X corresponds to aparameter (e.g., a UE ID) for determination of priority for configuringa representative AP (e.g., a UE ID may be set as n_(RNTI) and in thiscase, X=n_(RNTI) may be satisfied). In addition, since L is anaggregation level, L refers to the number of (E)CCEs used in one E-PDCCH(e.g., which may be represented by N^(CCE) _(EPDCCH) or N^(ECCE)_(EPDCCH)). min(a,b) refers to a minimum value of a and b. Z has a value1 or 2. In this regard, like in the example 1 or 3, when an interval ofAPs allocated to two (E)CCEs is 1 (e.g., in the case of AP indexes 7 and8 (or 107 and 108)), Z=1 may be given, and like in the example 2, whenan interval of APs allocated to two (E)CCEs is 2 (e.g., in the case ofAP indexes 7 and 9 (or 107 and 109)), Z=2 may be given.

Equations 7 and 8 below may be given in the same meaning as the methodof determining a representative AP according to Equation 6 above.

n′=n _(CCE) mod d)+(X mod min(L,d)) or

n′=(n _(ECCE) mod d)+(X mod min(L,d))  [Equation 7]

TABLE 8 Representative AP = p + n′*Z (p = 7 (or 107)) Example 1 Example2 Example 3 n′ (Z = 1) (Z = 2) (Z = 1) 0  7 (or 107) 7 (or 107) 7 (or107) 1  8 (or 108) 9 (or 109) 8 (or 108) 2  9 (or 109) — — 3 10 (or 110)— —

In Equation 7 and Table 8 above, n′ may correspond to a parameter fordetermination of an index of a resource region (e.g., (E)CCE) of anE-PDCCH, which is derived from a predetermined parameter X (e.g., anidentifier of a UE). For example, n′ may refer to a parameter fordetermination of a representative resource region (or a representative(E)CCE) index) of the E-PDCCH. That is, Equation 7 and Table 8 aboveshow that the representative AP corresponds (or is mapped) to arepresentative (E)CCE. In Table 8 above, as described above, the example1 corresponds to a case in which the number of resources (e.g., OFDMsymbols or resource elements) that can be used for an E-PDCCH in anormal CP subframe is equal to or greater than a predetermined referencevalue or a case in which the number of (E)CCEs defined in one PRB is 4,since Z=1 is satisfied, an interval between APs may be determined as 1.In Table 8 above, as described above, the example 2 corresponds to acase in which the number of resources that can be used for an E-PDCCH ina normal CP subframe is less than a predetermined reference value or acase in which the number of (E)CCEs defined in one PRB is 2, since Z=2,an interval between APs may be determined as 2. In Table 8, the example3 corresponds to a case of an extended CP subframe. In this case, sinceup to two APs may be used for an E-PDCCH and Z=1 is given, an intervalbetween APs may be determined as 1.

The parameter X may be a value (i.e., the parameter X is a value derivedfrom a UE ID) for determination of a representative AP by a UE ID. Forexample, when the UE ID is given as n_(RNTI), X may be given as afunction value Y_(k) used for determination of a search space of a PDCCHin a 3GPP LTE system. For example, Y_(k) may be determined by a UE ID(e.g., n_(RNTI)) according to Equation 8 below.

Y _(k)=(A·Y _(k-1))mod D,Y ⁻¹ =n _(RNTI)≠0  [Equation 8]

In Equation 8 above, k refers to a subframe index. A and D may bedetermined as appropriate numbers, for example, A=39827 and D=65537.

In Equations 5 and 6 above, when an aggregation level is 1 (that is,L=1), since a result of calculation X mod L is 0, the parameter X doesnot affect determination of the representative AP, and APs that aresequentially allocated according to positions of corresponding (E)CCEsof each PRB pair may be used as a representative AP. When an aggregationlevel is 1, one E-PDCCH constitutes one (E)CCE, and thus, an AP mappedto corresponding one (E)CCE is a representative AP.

In the case of L≥2, one (E)CCE present between a first (E)CCE and a last(E)CCE may be determined according to X, and an AP allocated (or mapped)to the one determined (E)CCE may be determined as a representative AP.

In Equations 5 and 6 above, X may be determined as a value derived froma parameter such as a UE ID, etc. However, alternatively, in order todirectly adjust selection of a representative AP, an eNB may directlyindicate a value to be used as X via a higher layer signal.

As described above, while a representative (E)CCE (or a representativeAP) used for detection of an E-PDCCH (or demodulation of an E-PDCCH) isselected, a plurality of E-PDCCH sets may be set for a UE.

For example, the eNB may configure two E-PDCCH sets (i.e., E-PDCCH set1and E-PDCCH set2) for one UE and may appropriately distribute an E-PDCCHcandidate monitored by the corresponding UE to the two E-PDCCH sets.Here, the two E-PDCCH sets may or may not overlap each other in a PRBregion, and parameters such as DMRS scrambling sequences, the number ofused PRBs, or the like may be differently set.

When the plural E-PDCCH sets are configured, a method of configuring arepresentative (E)CCE (or a representative AP) may be differentlydetermined for each respective E-PDCCH set. For example, when arepresentative AP is determined according to a function according toEquation 5 or 6 above, the parameter X used for determination of an APindex may be differently determined in the plural E-PDCCH sets. When areference for configuring a representative AP for a first UE isdifferently given for each respective E-PDCCH sets, even if the samereference as that of a second UE is used to select an AP in one E-PDCCH(e.g., E-PDCCH set1) among the plural E-PDCCH sets (i.e., when first andsecond UEs perform E-PDCCH demodulation using a DMRS of the same AP) andthus it is difficult to perform a MU-MIMO operation, a differentreference from that of the second UE is used to select an AP with highpossibility in another E-PDCCH set (e.g., when E-PDCCH set2) (i.e., whenthe first and second UEs perform E-PDCCH demodulation using DMRSs ofdifferent APs), and thus the MU-MIMO operation may be possible.

A parameter X (i.e., E-PDCCH set-specific) given for each respectiveE-PDCCH set may be derived from Y_(k) according to Equation 8 above. Forexample, a parameter X₁ for E-PDCCH set1 is given as Y_(k). On the otherhand, a parameter X₂ for E-PDCCH set2 may be determined in the form of avalue obtained by adding a predetermined number to X₁. A relationshipbetween X₁ and X₂ may be defined according to Equation 9 below.

X ₂ =X ₁ +G*M _(L,1)

In Equation 9 above, G is an integer that is equal to or greater than 1,and M_(L,1) is the number of E-PDCCH candidates of an aggregation levelL present in E-PDCCH set1. According to Equation 9 above, when a methodof continuously distributing search spaces of E-PDCCH set1 and E-PDCCHset2 is applied, a start (E)CCE index of a search space is used as areference for selection of a representative AP in each E-PDCCH set.

For another example, both X₁ and X₂ for E-PDCCHs set1 and set2 aredetermined according to Equation 8 above. However, parameters A and/or Dof Equation 8 may be differently set for X₁ and X₂ such that differentX₁ and X₂ may be derived from the same UE ID (e.g., n_(RNTI)). Throughthis process, one UE may select a representative (E)CCE (or arepresentative AP) using different references for different E-PDCCH setsand perform E-PDCCH detection (or demodulation) using an RScorresponding to the selected representative AP.

As described above, a PUCCH resource linked with the selected/determinedrepresentative AP (or representative (E)CCE) may be used for ACK/NACKfeedback. For example, when the representative AP is determinedaccording to Equation 5 or 6 above, the representative (E)CCE isdetermined and an AP corresponding (or mapped) to the determinedrepresentative (E)CCE is determined as a representative AP. That is, therepresentative (E)CCE may correspond to a portion (i.e., n′ of Equation7) obtained by excluding p from Equation 5 or 6 above. For example, asthe representative AP is determined by adding a minimum value (7 or 107)of an AP to n′, n′ and a representative (E)CCE index n* may bedetermined according to a one-to-one mapping relationship. When therepresentative (E)CCE is determined, a PUCCH linked with therepresentative (E)CCE may be used for ACK/NACK feedback.

For example, in the examples as a method of determining a PUCCH resourceassociated with an E-PDCCH, it is assumed that the UE determines aspecific (E)CCE index n* among L (L=aggregation level) (E)CCEs,determine a PUCCH resource (e.g., n*+k+N_(offset) ^(PUCCH)) linked withan (E)CCE index n*+k obtained by applying predetermined offset (e.g., k)to the specific (E)CCE index, and feedback ACK/NACK.

Here, when the specific (E)CCE index n* is determined, n′ in Equation 7above may be considered. That is, the specific (E)CCE index n* may bedetermined as an index corresponding to n′ determined in considerationof a UE ID (here, n′ may be defined according to Equation 7 above). kcorresponding to the predetermined offset may be indicated using aspecific field of a DCI format of DL assignment. N_(offset) ^(PUCCH) maybe an offset value indicating a start point of a PUCCH resource regionand provided via higher layer signaling such as an RRC, etc. Inaddition, when one UE performs ACK/NACK transmission using two PUCCHresources, an index of a first PUCCH resource may be determined asn*+k+N_(offset) ^(PUCCH) and an index of a second PUCCH resource may bedetermined as n*+k+N_(offset) ^(PUCCH)+1.

FIGS. 9 and 10 are flowcharts for explanation of an E-PDCCH-basedoperation method according to embodiments of the present invention.

An example of FIG. 9 relates to a method of determining an E-PDCCHrepresentative AP and performing E-PDCCH transmission and receptionaccording to the determined E-PDCCH representative AP.

In step S911 of FIG. 9, an eNB may determine a resource region to whichan E-PDCCH is mapped for E-PDCCH transmission to a specific UE. Here,the eNB may determine a representative AP index corresponding (ormapped) to a representative (E)CCE index among resource regions to whichan E-PDCCH is mapped. A method of determining the representative (E)CCEand/or the representative AP may be based on the aforementioned examplesof the present invention. For example, the representative AP may bedetermined to correspond to a representative (E)CCE (e.g., n′ ofEquation 7 above) determined based on an identifier of the UE.

In step S912, the eNB may map an E-PDCCH to a resource element andtransmit the E-PDCCH to the specific UE.

In step S921, the UE may determine a representative (E)CCE frominformation about a resource region in which the E-PDCCH is transmittedand determine a representative AP corresponding to the representative(E)CCE for E-PDCCH monitoring (i.e., decoding attempt). A method ofdetermining the representative (E)CCE and/or the representative AP maybe based on the aforementioned examples of the present invention. Forexample, the representative AP may be determined to correspond to therepresentative (E)CCE (e.g., n′ in Equation 7 above) determined based onan identifier of the UE.

In step S922, the UE may perform E-PDCCH demodulation using therepresentative AP. For example, the UE may perform E-PDCCH demodulationusing a channel estimated based on a DMRS corresponding to therepresentative AP.

The example of FIG. 10 relates to a method of determining a PUCCHresource when the UE feedbacks ACK/NACK information to transmission of aPDSCH indicated by an E-PDCCH to the eNB.

Steps S1011 and S1012 of FIG. 10 correspond to steps S911 and S912 ofFIG. 9, and steps S1021 and S1022 of FIG. 10 correspond to steps S921and S922 of FIG. 9. Thus, repeated descriptions are not given here.

In step S1013, the eNB may transmit DL data through a PDSCH scheduledaccording to DL assignment DCI transmitted through the E-PDCCH to theUE.

In step S1023, the UE may decode the PDSCH and generate ACK/NACKinformation according to whether decoding is successful.

In step S1024, the UE may determine a PUCCH resource (e.g., PUCCH format1a/1b resources) for transmission of the generated ACK/NACK information.Here, the UE may determine a representative (E)CCE (e.g., n′ in Equation7 above) determined based on a identifier of the UE among (E)CCEs of anE-PDCCH associated with the PDSCH and determine a PUCCH resourcecorresponding to the representative (E)CCE.

In step S1025, the UE may transmit ACK/NACK information using thedetermined PUCCH resource to the eNB.

In step S1014, the eNB may receive the ACK/NACK information from the UE.From a viewpoint of the eNB, the eNB may determine a PUCCH resourceusing the same method as a method of determining a PUCCH resource fortransmission of the ACK/NACK information by the UE and attempt toreceive the ACK/NACK information.

Descriptions of the aforementioned various embodiments of the presentinvention can be independently applied or two or more embodiments can besimultaneously applied, and a repeated description is not given forclarity.

According to the various embodiments of the present invention, a DLtransmission entity or a UL reception entity is mainly an eNB and a DLreception entity or a UL transmission entity is mainly a UE. However,the scope of the present invention is not limited thereto. That is, theaforementioned principle of the various embodiments of the presentinvention can also be applied to a case in which a relay is a DLtransmission entity to the UE or a UL reception entity from the UE, or acase in which when a relay is a UL transmission entity to the eNB or aDL reception entity from the eNB.

FIG. 11 illustrates configurations of an eNB 1110 and a UE 1120according to an embodiment of the present invention.

Referring to FIG. 11, the eNB 1110 may include a transmitter 1111, areceiver 1112, a processor 1113, a memory 1114, and a plurality ofantennas 1115. The plural antennas 1115 represents that the eNB 1110supports MIMO transmission/reception. The transmitter 1111 may transmitsignals, data and information to external apparatuses (e.g., UEs). Thereceiver 1112 may receive signals, data, and information from externalapparatuses (e.g., UEs). The processor 1113 may control an overalloperation of the eNB 1110.

According to an embodiment of the present invention, the eNB 1110 may beconfigured to transmit a DL control channel (e.g., an E-PDCCH). Theprocessor 1113 of the eNB 1110 may be configured to determine oneantenna port (i.e., a representative AP) used for the UL controlchannel. In addition, the processor 1113 may be configured to map the DLcontrol channel to a resource element using the one determined antennaport. In addition, the processor 1113 may be configured to transmit themapped DL control channel to the UE 1120 using the transmitter 1111.Here, an index of the one antenna port (i.e., a representative AP) maybe determined according to various methods according to the presentinvention. For example, one representative AP index may be determinedbased on an (E)CCE index derived from an identifier of the UE 1120.

According to another embodiment of the present invention, the eNB 1110may be configured to receive ACK/NACK information. The processor 1113 ofthe eNB 1110 may be configured to transmit a DL control channel (e.g.,an E-PDCCH) for carrying scheduling information of DL data and a DL datachannel indicated by the DL control channel to the UE 1120 using thetransmitter 1111. The processor 1113 may be configured to receiveACK/NACK feedback information to the DL data channel from the UE 1120through a UL control channel (e.g., PUCCH) resource using a receiver1122. Here, an index of the PUCCH may be determined using theaforementioned various methods according to the present invention. Forexample, the index of the PUCCH resource may be determined based on an(E)CCE index derived from an identifier of the UE 1120.

The processor 1113 of the eNB 1110 may also perform a function ofcalculation-processing information received by the eNB 1110, informationto be externally transmitted, etc., and the memory 1114 may store thecalculation-processed information, etc. for a predetermined period oftime and may be replaced with a component such as a buffer (not shown).

Referring to FIG. 11, the UE 1120 according to the present invention mayinclude a transmitter 1121, a receiver 1122, a processor 1123, a memory1124, and a plurality of antennas 1125. The plural antennas 1125 mayrefer to a UE apparatus for supporting MIMO transmission and reception.The transmitter 1121 may transmit various signals, data, and informationto an external apparatus (e.g., an eNB). The receiver 1122 may receivevarious signals, data, and information from an external apparatus (e.g.,an eNB). The processor 1123 may control an overall operation of the UE1120.

According to an embodiment of the present invention, the UE 1120 may beconfigured to receive a DL control channel (e.g., an E-PDCCH). Theprocessor 1123 of the UE 1120 may be configured to determine one antennaport (i.e., a representative AP) used for the DL control channel. Inaddition, the processor 1123 may receive the DL control channel throughthe receiver 1122 using the one antenna port, and demodulation of the DLcontrol channel may be based on an RS (a UE-specific RS or DMRS) for theone antenna port. Here, an index of the one antenna port (i.e., arepresentative AP) may be determined according to the aforementionedvarious methods of the present invention. For example, the index of theone representative AP may be determined based on the (E)CCE indexderived from an identifier of the UE 1120.

According to another embodiment of the present invention, the UE 1120may be configured to transmit ACK/NACK information. The processor 1123of the UE 1120 may be configured to transmit ACK/NACK information to aDL data channel through the transmitter 1121 using a UL control channelresource. Here, the index of the PUCCH may be determined using theaforementioned various methods of the present invention. For example,the index of the PUCCH resource may be determined based on the (E)CCEindex derived from the identifier of the UE 1120.

The processor 1123 of the UE 1120 may calculate and process informationreceived by the UE 1120, information to be transmitted to the outside,etc. The memory 1124 may store the calculated and processed informationfor a predetermined time and may be replaced by a component such as abuffer (not shown).

The detailed configurations of the eNB 1110 and the 1120 may beimplemented such that the aforementioned embodiments of the presentinvention can be independently applied thereto or two or moreembodiments can be simultaneously applied thereto, description ofredundant parts is omitted for clarity.

Description of the eNB 1110 in FIG. 13 may be equally applied to anapparatus as a downlink transmitter or an uplink receiver anddescription of the UE 1120 may be equally applied to a relay as adownlink receiver or an uplink transmitter.

The embodiments of the present invention may be implemented by variousmeans, for example, hardware, firmware, software, or combinationsthereof.

When the embodiments of the present invention are implemented usinghardware, the embodiments may be implemented using at least one ofapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the embodiments of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. For example, software code may be stored in a memory unitand executed by a processor. The memory unit is located at the interioror exterior of the processor and may transmit and receive data to andfrom the processor via various known means.

The detailed description of the preferred embodiments of the presentinvention is given to enable those skilled in the art to realize andimplement the present invention. While the present invention has beendescribed referring to the preferred embodiments of the presentinvention, those skilled in the art will appreciate that manymodifications and changes can be made to the present invention withoutdeparting from the spirit and essential characteristics of the presentinvention. For example, the structures of the above-describedembodiments of the present invention can be used in combination. Theabove embodiments are therefore to be construed in all aspects asillustrative and not restrictive. Therefore, the present inventionintends not to limit the embodiments disclosed herein but to give abroadest range matching the principles and new features disclosedherein.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. Therefore, the present invention intends not tolimit the embodiments disclosed herein but to give a broadest rangematching the principles and new features disclosed herein. It is obviousto those skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim by asubsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The above-described embodiments of the present invention can be appliedto various mobile communication systems.

What is claimed is:
 1. A method of transmitting an Enhanced PhysicalDownlink Control Channel (EPDCCH) by an evolved nodeB (eNB) in awireless communication system, the method comprising: transmitting theEPDCCH to a user equipment (UE) through one antenna port, wherein anindex of the one antenna port is determined based on a value n′satisfying the following equation,n′=(nECCE mod d)+(X mod min(L,d)), wherein, nECCE is a lowest ECCE indexused for transmission of the EPDCCH; d is a number of ECCEs per resourceblock pair; X is an identifier of the UE; L is a number of ECCEs usedfor the EPDCCH; mod is modulo function; and min (L,d) is a minimum valueof L and d.
 2. The method according to claim 1, further comprising:mapping the EPDCCH to resource elements before the transmitting.
 3. Amethod of receiving an Enhanced Physical Downlink Control Channel,EPDCCH, by a user equipment (UE) in a wireless communication system, themethod comprising: determining one antenna port used for the EPDCCH; anddemodulating the EPDCCH based on a reference signal for the one antennaport, and wherein an index of the one antenna port is determined basedon a value n′ satisfying the following equation,n′=(nECCE mod d)+(X mod min(L,d)), wherein, nECCE is a lowest ECCE indexused for transmission of the EPDCCH; d is a number of ECCEs per resourceblock pair; X is an identifier of the UE; L is a number of ECCEs usedfor the EPDCCH; mod is modulo function; and min (L,d) is a minimum valueof L and d.
 4. An evolved NodeB (eNB) for transmitting an EnhancedPhysical Downlink Control Channel (EPDCCH) in a wireless communicationsystem, the eNB comprising: a processor configured to: a transmitterconfigured to transmit the EPDCCH to a user equipment (UE)) through oneantenna port; wherein an index of the one antenna port is determinedbased on a value n′ satisfying the following equation,n′=(nECCE mod d)+(X mod min(L,d)), wherein, nECCE is a lowest ECCE indexused for transmission of the EPDCCH; d is a number of ECCEs per resourceblock pair; X is an identifier of the UE; L is a number of ECCEs usedfor the EPDCCH; mod is modulo function; and min (L,d) is a minimum valueof L and d.
 5. The eNB according to claim 4, wherein the processorfurther configured to map the EPDCCH to resource elements before thetransmission.
 6. A user equipment (UE) for receiving an EnhancedPhysical Downlink Control Channel, EPDCCH, in a wireless communicationsystem, the UE comprising: a processor configured to: determine oneantenna port used for the EPDCCH, and demodulate the EPDCCH based on areference signal for the one antenna port; wherein an index of the oneantenna port is determined based on a value n′ satisfying the followingequation,n′=(nECCE mod d)+(X mod min(L,d)), wherein, nECCE is a lowest ECCE indexused for transmission of the EPDCCH; d is a number of ECCEs per resourceblock pair; X is an identifier of the UE; L is a number of ECCEs usedfor the EPDCCH; mod is modulo function; and min (L,d) is a minimum valueof L and d.